diff --git a/src/game/card.ts b/src/game/card.ts
index 0a52410..26df685 100644
--- a/src/game/card.ts
+++ b/src/game/card.ts
@@ -1,77 +1,24 @@
-type CardValue = -2 | -1 | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12;
+export type Card =
+  | -2
+  | -1
+  | 0
+  | 1
+  | 2
+  | 3
+  | 4
+  | 5
+  | 6
+  | 7
+  | 8
+  | 9
+  | 10
+  | 11
+  | 12;
 
-export type ObfuscatedCardValue = CardValue | "X";
+export type ConcealableCard = Card | null;
 
-type CardColor =
-  | "darkblue"
-  | "lightblue"
-  | "green"
-  | "yellow"
-  | "red"
-  | "black";
-
-// TODO: use smarter types like Omit<>, Pick<>, etc.
-export type ObfuscatedCard = {
-  id: number;
-  name: string;
-  value: ObfuscatedCardValue;
-  color: CardColor;
-};
-
-export class Card {
-  id: number;
-  name: string;
-  value: CardValue;
-  color: CardColor;
-  constructor(id: number, value: CardValue) {
-    this.id = id;
-    this.value = value;
-    this.name = `${value} Card`;
-    this.color = this.matchColorToCardValue(value);
-  }
-
-  matchColorToCardValue(value: CardValue | ObfuscatedCardValue): CardColor {
-    switch (value) {
-      case -2:
-        return "darkblue";
-      case -1:
-        return "darkblue";
-      case 0:
-        return "lightblue";
-      case 1:
-        return "green";
-      case 2:
-        return "green";
-      case 3:
-        return "green";
-      case 4:
-        return "green";
-      case 5:
-        return "yellow";
-      case 6:
-        return "yellow";
-      case 7:
-        return "yellow";
-      case 8:
-        return "yellow";
-      case 9:
-        return "red";
-      case 10:
-        return "red";
-      case 11:
-        return "red";
-      case 12:
-        return "red";
-      case "X":
-        return "black";
-      default:
-        return "red";
-    }
-  }
-}
-
-export type ObfuscatedCardStack = {
-  cards: ObfuscatedCard[];
+export type ConcealableCardStack = {
+  cards: ConcealableCard[];
 };
 
 export class CardStack {
@@ -84,77 +31,77 @@ export class CardStack {
   generateCards() {
     for (let cardNumber = 1; cardNumber <= 150; cardNumber++) {
       if (cardNumber <= 5) {
-        this.cards.push(new Card(cardNumber, -2));
+        this.cards.push(-2);
         continue;
       }
 
       if (cardNumber > 5 && cardNumber <= 15) {
-        this.cards.push(new Card(cardNumber, -1));
+        this.cards.push(-1);
         continue;
       }
 
       if (cardNumber > 15 && cardNumber <= 30) {
-        this.cards.push(new Card(cardNumber, 0));
+        this.cards.push(0);
         continue;
       }
 
       if (cardNumber > 30 && cardNumber <= 40) {
-        this.cards.push(new Card(cardNumber, 1));
+        this.cards.push(1);
         continue;
       }
 
       if (cardNumber > 40 && cardNumber <= 50) {
-        this.cards.push(new Card(cardNumber, 2));
+        this.cards.push(2);
         continue;
       }
 
       if (cardNumber > 50 && cardNumber <= 60) {
-        this.cards.push(new Card(cardNumber, 3));
+        this.cards.push(3);
         continue;
       }
 
       if (cardNumber > 60 && cardNumber <= 70) {
-        this.cards.push(new Card(cardNumber, 4));
+        this.cards.push(4);
         continue;
       }
 
       if (cardNumber > 70 && cardNumber <= 80) {
-        this.cards.push(new Card(cardNumber, 5));
+        this.cards.push(5);
         continue;
       }
 
       if (cardNumber > 80 && cardNumber <= 90) {
-        this.cards.push(new Card(cardNumber, 6));
+        this.cards.push(6);
         continue;
       }
 
       if (cardNumber > 90 && cardNumber <= 100) {
-        this.cards.push(new Card(cardNumber, 7));
+        this.cards.push(7);
         continue;
       }
 
       if (cardNumber > 100 && cardNumber <= 110) {
-        this.cards.push(new Card(cardNumber, 8));
+        this.cards.push(8);
         continue;
       }
 
       if (cardNumber > 110 && cardNumber <= 120) {
-        this.cards.push(new Card(cardNumber, 9));
+        this.cards.push(9);
         continue;
       }
 
       if (cardNumber > 120 && cardNumber <= 130) {
-        this.cards.push(new Card(cardNumber, 10));
+        this.cards.push(10);
         continue;
       }
 
       if (cardNumber > 130 && cardNumber <= 140) {
-        this.cards.push(new Card(cardNumber, 11));
+        this.cards.push(11);
         continue;
       }
 
       if (cardNumber > 140 && cardNumber <= 150) {
-        this.cards.push(new Card(cardNumber, 12));
+        this.cards.push(12);
         continue;
       }
     }
diff --git a/src/game/events.ts b/src/game/events.ts
index 3c300f3..daf07a8 100644
--- a/src/game/events.ts
+++ b/src/game/events.ts
@@ -4,8 +4,27 @@ import { Game } from "./game";
 
 import { allGames } from "./game";
 
-export const handleJoinSession = (socket: Socket, sessionId: string) => {
+type SessionResponse = "success" | "error:full" | "error:running";
+
+export const handleJoinSession = (
+  socket: Socket,
+  sessionId: string,
+  callback: Function
+) => {
+  const isSessionRunning = allGames.some(
+    (game) => game.sessionId === sessionId
+  );
+  if (isSessionRunning) {
+    callback("error:running" satisfies SessionResponse);
+    socket.emit(
+      "message",
+      "A Game is already running in this session. Please join another session."
+    );
+    return;
+  }
+
   socket.join(sessionId);
+  callback("success" satisfies SessionResponse);
   console.log("User joined session:", sessionId);
 
   const numberOfClients = io.sockets.adapter.rooms.get(sessionId)?.size ?? 0;
@@ -41,6 +60,7 @@ export const handleNewGame = (
 
   if (players && players.size > 1) {
     const game = new Game(socket, sessionId, players);
+    removeOldGame(sessionId);
     allGames.push(game);
     console.log(`New Game created with ${game.playerCount} players!`);
     game.gameLoop();
@@ -62,3 +82,12 @@ export const handleDisconnect = (socket: Socket) => {
     io.to(sessionName).emit("clients-in-session", socketIds.size);
   });
 };
+
+const removeOldGame = (sessionId: string) => {
+  const oldGameIndex = allGames.findIndex(
+    (game) => game.sessionId === sessionId
+  );
+  if (oldGameIndex !== -1) {
+    allGames.splice(oldGameIndex, 1);
+  }
+};
diff --git a/src/game/game.ts b/src/game/game.ts
index 5b24c09..e01b94d 100644
--- a/src/game/game.ts
+++ b/src/game/game.ts
@@ -1,6 +1,6 @@
-import { Player, ObfuscatedPlayer } from "./player";
-import { CardStack } from "./card";
-import { Card, ObfuscatedCardStack } from "./card";
+import { Player, ObfuscatedPlayer, ConcealableColumn } from "./player";
+import { CardStack, ConcealableCard } from "./card";
+import { Card, ConcealableCardStack } from "./card";
 import { Socket } from "socket.io";
 import { io } from "../server";
 
@@ -18,14 +18,14 @@ type PlayerAction<ActionDataType> = {
   data: ActionDataType;
 };
 
-type CardPosition = number;
+type CardPosition = [number, number];
 
 // obfuscated types are used to send only necessary data to the client
 export type ObfuscatedGame = {
   sessionId: string;
   playerCount: number;
   players: ObfuscatedPlayer[];
-  cardStack: ObfuscatedCardStack;
+  cardStack: ConcealableCardStack;
   discardPile: Card[];
   phase: string;
   round: number;
@@ -78,13 +78,8 @@ export class Game {
     let index = 0;
     playerIds.forEach((socketId) => {
       index++;
-      const playerCards = cardStack.cards.splice(0, 12);
-      const player = new Player(
-        index,
-        socketId,
-        `Player ${index}`,
-        playerCards
-      );
+
+      const player = new Player(index, socketId, `Player ${index}`, cardStack);
       players.push(player);
     });
 
@@ -98,8 +93,8 @@ export class Game {
     this.cardStack = new CardStack();
     this.cardStack.shuffleCards();
     this.players.forEach((player) => {
-      player.cards = this.cardStack.cards.splice(0, 12);
-      player.knownCardPositions = new Array(12).fill(false);
+      player.deck = player.generateDeck(this.cardStack);
+      player.knownCardPositions = player.createUnknownCardPositions();
       player.playersTurn = true;
       player.cardCache = null;
       player.tookDispiledCard = false;
@@ -117,6 +112,7 @@ export class Game {
     this.sendObfuscatedGameUpdate();
     while (this.phase !== gamePhase.gameEnded) {
       this.checkForFullRevealedCards();
+      this.removeThreeOfAKinds();
       switch (this.phase) {
         case gamePhase.revealTwoCards:
           console.log("\nGame phase: revealTwoCards");
@@ -245,12 +241,15 @@ export class Game {
 
   // Player Action Callbacks
 
-  revealCardAction(playerSocketId: string, cardPosition: number) {
+  revealCardAction(playerSocketId: string, cardPosition: CardPosition) {
     const player = this.getPlayerBySocketId(playerSocketId);
-    const revealedCard = player.cards[cardPosition];
-    console.log(`Revealed card ${revealedCard} at position ${cardPosition}`);
+    const [columnIndex, cardIndex] = cardPosition;
+    const revealedCard = player.deck[columnIndex][cardIndex];
+    console.log(
+      `Revealed card ${revealedCard} at column ${columnIndex} card ${cardIndex}`
+    );
     const playerIndex = this.players.indexOf(player!);
-    this.players[playerIndex].knownCardPositions[cardPosition] = true;
+    this.players[playerIndex].knownCardPositions[columnIndex][cardIndex] = true;
     this.sendObfuscatedGameUpdate();
   }
 
@@ -281,15 +280,17 @@ export class Game {
     this.sendObfuscatedGameUpdate();
   }
 
-  placeCardAction(playerSocketId: string, cardPosition: number) {
+  placeCardAction(playerSocketId: string, cardPosition: CardPosition) {
     const player = this.getPlayerBySocketId(playerSocketId);
     console.log(`Player ${player.name} placed a card.`);
     const placedCard = player.cardCache!;
     player.cardCache = null;
-    const replacedCard = player.cards[cardPosition];
+    const [columnIndex, cardIndex] = cardPosition;
+    const replacedCard = player.deck[columnIndex][cardIndex];
     this.discardPile.push(replacedCard);
-    player.cards[cardPosition] = placedCard;
-    player.knownCardPositions[cardPosition] = true;
+    player.deck[columnIndex][cardIndex] = placedCard;
+    player.knownCardPositions[columnIndex][cardIndex] = true;
+    // TODO: check for three of a kind
     this.nextPlayersTurn();
     this.phase = gamePhase.pickUpCard;
     this.sendObfuscatedGameUpdate();
@@ -379,32 +380,24 @@ export class Game {
       phase: this.phase,
       round: this.round,
       discardPile: this.discardPile,
-      players: this.players.map(({ cards, ...player }) => {
+      players: this.players.map(({ deck, ...player }) => {
         return {
           ...player,
-          cards: cards.map((card: Card, index: number) => {
-            // unknown cards are obfuscated to X
-            return {
-              id: player.knownCardPositions[index] ? card.id : 0,
-              value: player.knownCardPositions[index] ? card.value : "X",
-              name: player.knownCardPositions[index]
-                ? card.name
-                : "Facedown Card",
-              color: player.knownCardPositions[index] ? card.color : "black",
-              matchColorToCardValue: card.matchColorToCardValue,
-            };
+          deck: deck.map((column, columnIndex) => {
+            const concealableColumn = column.map((card, cardIndex) => {
+              // unknown cards are obfuscated to null
+              return player.knownCardPositions[columnIndex][cardIndex]
+                ? card
+                : (null as ConcealableCard);
+            });
+            return concealableColumn as ConcealableColumn;
           }),
-        };
+        } satisfies ObfuscatedPlayer;
       }),
       cardStack: {
         cards: this.cardStack.cards.map((card: Card) => {
           // player may not see the value of the facedown cards in the cardStack
-          return {
-            id: 0,
-            value: "X",
-            name: "Facedown Card",
-            color: "black",
-          };
+          return null;
         }),
       },
     };
@@ -419,13 +412,7 @@ export class Game {
   updatePlayerRoundPoints() {
     this.players.forEach((player) => {
       const revealedCardValuesSum = player.getRevealedCardsValueSum();
-      const threeOfAKinds = player.getThreeOfAKinds();
-      const threeOfAKindPoints = threeOfAKinds.reduce(
-        (points, threeOfAKind) => points + threeOfAKind.value * 3,
-        0
-      );
-
-      player.roundPoints = revealedCardValuesSum - threeOfAKindPoints;
+      player.roundPoints = revealedCardValuesSum;
     });
   }
 
@@ -481,8 +468,8 @@ export class Game {
     if (alreadyClosedPlayers.length > 0) return; // TODO: check if this is correct with more than 2 players
 
     const playerWithAllCardsRevealed = this.players.find((player) =>
-      player.knownCardPositions.every(
-        (knownCardPosition) => knownCardPosition === true
+      player.knownCardPositions.every((knownCardsColumn) =>
+        knownCardsColumn.every((knownCard) => knownCard === true)
       )
     );
     if (playerWithAllCardsRevealed) {
@@ -490,6 +477,22 @@ export class Game {
     }
   }
 
+  removeThreeOfAKinds() {
+    this.players.forEach((player) => {
+      const threeOfAKinds = player.getThreeOfAKinds();
+      if (threeOfAKinds.length == 0) return;
+      threeOfAKinds.forEach((threeOfAKind) => {
+        const { columnIndex, value } = threeOfAKind;
+        this.discardPile.push(value as Card);
+        this.discardPile.push(value as Card);
+        this.discardPile.push(value as Card);
+        player.deck.splice(columnIndex, 1);
+        player.knownCardPositions.splice(columnIndex, 1);
+      });
+      this.sendObfuscatedGameUpdate();
+    });
+  }
+
   checkIfPointLimitReached() {
     const highestPoints = Math.max(
       ...this.players.map((player) => player.totalPoints)
@@ -553,9 +556,11 @@ export class Game {
 
   revealAllCards() {
     this.players.forEach((player) => {
-      player.knownCardPositions = player.knownCardPositions.map(
-        (knownCardPosition) => true
-      );
+      player.knownCardPositions.forEach((column, columnIndex) => {
+        column.forEach((card, cardIndex) => {
+          player.knownCardPositions[columnIndex][cardIndex] = true;
+        });
+      });
     });
   }
 
@@ -650,16 +655,6 @@ export class Game {
     else throw new Error(`No player with socketId ${playerSocketId} found!`);
   }
 
-  listPlayerSocketListeners() {
-    console.log("Player socket listeners:");
-    io.sockets.sockets.forEach((socket) => {
-      console.log(socket.id);
-      socket.eventNames().forEach((eventName) => {
-        console.log(`${eventName.toString()}`);
-      });
-    });
-  }
-
   sendMessageToAllPlayers(message: string) {
     io.to(this.sessionId).emit("message", message);
     console.log(`Sent Message (Session): ${message}`);
diff --git a/src/game/player.ts b/src/game/player.ts
index a88fd1c..b6cb92a 100644
--- a/src/game/player.ts
+++ b/src/game/player.ts
@@ -1,11 +1,30 @@
-import { Card, ObfuscatedCard } from "./card";
+import { Card, CardStack, ConcealableCard } from "./card";
+
+type Column = [Card, Card, Card];
+type Deck = Column[];
+
+export type ConcealableColumn = [
+  ConcealableCard,
+  ConcealableCard,
+  ConcealableCard
+];
+type ConcealableDeck = ConcealableColumn[];
+
+type ColumnIndex = number;
+
+type ThreeOfAKind = {
+  columnIndex: ColumnIndex;
+  value: number;
+};
+
+type KnownCardsColumn = [boolean, boolean, boolean];
 
 export type ObfuscatedPlayer = {
   id: number;
   socketId: string;
   name: string;
-  cards: ObfuscatedCard[];
-  knownCardPositions: boolean[];
+  deck: ConcealableDeck;
+  knownCardPositions: KnownCardsColumn[];
   playersTurn: boolean;
   cardCache: Card | null;
   tookDispiledCard: boolean;
@@ -14,26 +33,12 @@ export type ObfuscatedPlayer = {
   closedRound: boolean;
 };
 
-type ColumnPosition = [number, number, number];
-
-type ThreeOfAKind = {
-  position: ColumnPosition;
-  value: number;
-};
-
-const COLUMN_POSITIONS: ColumnPosition[] = [
-  [0, 4, 8],
-  [1, 5, 9],
-  [2, 6, 10],
-  [3, 7, 11],
-];
-
 export class Player {
   id: number;
   socketId: string;
   name: string;
-  cards: Card[];
-  knownCardPositions: boolean[];
+  deck: Deck;
+  knownCardPositions: KnownCardsColumn[];
   playersTurn: boolean;
   cardCache: Card | null; // this is where the card is temporarily stored when a player draws a card
   tookDispiledCard: boolean; // this is used to check if a player took a dispiled card in the current turn
@@ -41,12 +46,17 @@ export class Player {
   totalPoints: number;
   closedRound: boolean;
   place: number | null; // indicates the place the player got in the last round
-  constructor(id: number, socketId: string, name: string, cards: Card[]) {
+  constructor(
+    id: number,
+    socketId: string,
+    name: string,
+    cardStack: CardStack
+  ) {
     this.id = id;
     this.socketId = socketId;
     this.name = name;
-    this.cards = cards;
-    this.knownCardPositions = new Array(12).fill(false);
+    this.deck = this.generateDeck(cardStack);
+    this.knownCardPositions = this.createUnknownCardPositions();
     this.playersTurn = true;
     this.cardCache = null;
     this.tookDispiledCard = false;
@@ -56,74 +66,79 @@ export class Player {
     this.place = null;
   }
 
+  generateDeck(cardStack: CardStack): Deck {
+    const deck: Deck = [];
+    for (let i = 0; i < 4; i++) {
+      deck.push(cardStack.cards.splice(0, 3) as Column);
+    }
+    return deck;
+  }
+
+  createUnknownCardPositions(): KnownCardsColumn[] {
+    const knownCardPositions: KnownCardsColumn[] = [];
+    for (let i = 0; i < 4; i++) {
+      knownCardPositions.push([false, false, false]);
+    }
+    return knownCardPositions;
+  }
+
   hasInitialCardsRevealed(): boolean {
-    const revealedCards = this.knownCardPositions.filter(
-      (knownCard) => knownCard === true
+    const flattenedKnownCardPositions = this.knownCardPositions.flat();
+    const revealedCards = flattenedKnownCardPositions.filter(
+      (position) => position
     );
     if (revealedCards.length > 1) return true;
     else return false;
   }
 
   getRevealedCardCount(): number {
-    return this.knownCardPositions.filter((position) => position).length;
+    return this.knownCardPositions.flat().filter((position) => position == true)
+      .length;
   }
 
   getThreeOfAKinds(): ThreeOfAKind[] {
-    const revealedCardPositions = this.getRevealedCardPositions();
-    const columns: ColumnPosition[] = COLUMN_POSITIONS;
     const threeOfAKinds: ThreeOfAKind[] = [];
-    columns.forEach((column) => {
-      const columnValues = column.map((position) => this.cards[position].value);
-      const columnHasSameValues = columnValues.every(
-        (value) => value === columnValues[0]
+    this.deck.forEach((column, index) => {
+      const firstCard = column[0];
+      const columnIndex = index;
+
+      const columnHasSameCards = column.every((card) => card === firstCard);
+      const columnIsRevealed = this.knownCardPositions[columnIndex].every(
+        (isCardRevealed) =>
+          isCardRevealed === this.knownCardPositions[columnIndex][0]
       );
-      const columnIsRevealed = column.every((position) =>
-        revealedCardPositions.includes(position)
-      );
-      if (columnHasSameValues && columnIsRevealed) {
+
+      if (columnHasSameCards && columnIsRevealed) {
         threeOfAKinds.push({
-          position: column,
-          value: columnValues[0],
+          columnIndex: columnIndex as ColumnIndex,
+          value: firstCard,
         });
       }
     });
     return threeOfAKinds;
   }
 
-  getRevealedCardPositions(): number[] {
-    const revealedCardPositions: number[] = [];
-    this.knownCardPositions.forEach((position, index) => {
-      if (position) revealedCardPositions.push(index);
-    });
-    return revealedCardPositions;
-  }
-
   getRevealedCards(): Card[] {
     const revealedCards: Card[] = [];
-    this.knownCardPositions.forEach((position, index) => {
-      if (position) revealedCards.push(this.cards[index]);
+    this.knownCardPositions.forEach((column, columnIndex) => {
+      column.forEach((isCardRevealed, cardIndex) => {
+        if (isCardRevealed)
+          revealedCards.push(this.deck[columnIndex][cardIndex]);
+      });
     });
     return revealedCards;
   }
 
   getRevealedCardsValueSum(): number {
     const revealedCards = this.getRevealedCards();
-    const revealedCardsValueSum = revealedCards.reduce(
-      (sum, card) => sum + card.value,
-      0
-    );
+    let revealedCardsValueSum = 0;
+    revealedCards.forEach((card) => (revealedCardsValueSum += card));
     return revealedCardsValueSum;
   }
 
   getHighestRevealedCardValue(): number {
     const revealedCards = this.getRevealedCards();
-    const highestRevealedCardValue = revealedCards.reduce(
-      (highestValue, card) => {
-        if (card.value > highestValue) return card.value;
-        else return highestValue;
-      },
-      0
-    );
+    const highestRevealedCardValue = Math.max(...revealedCards);
     return highestRevealedCardValue;
   }
 }
diff --git a/src/server.ts b/src/server.ts
index cbe65e2..1f1bcc4 100644
--- a/src/server.ts
+++ b/src/server.ts
@@ -34,8 +34,8 @@ export const io = new SocketIOServer(httpServer, {
 io.on("connection", (socket: Socket) => {
   console.log("A user connected:", socket.id);
 
-  socket.on("join-session", (sessionId: string) =>
-    handleJoinSession(socket, sessionId)
+  socket.on("join-session", (sessionId: string, callback) =>
+    handleJoinSession(socket, sessionId, callback)
   );
 
   socket.on("leave-session", (sessionId: string) => {