diff --git a/packages/engine/src/game.ts b/packages/engine/src/game.ts
index 67baafb..231a63c 100644
--- a/packages/engine/src/game.ts
+++ b/packages/engine/src/game.ts
@@ -226,7 +226,7 @@ export interface CastParams {
 }
 
 /** The revision new games are dealt under; GameConfig.deckRev pins it per game. */
-export const CURRENT_RULES_REV = 3;
+export const CURRENT_RULES_REV = 4;
 
 export interface GameConfig {
   playerIds: PlayerId[];
@@ -245,6 +245,9 @@ export interface GameConfig {
    * Rev 3: VISIONSTONE pierces its one wall for every sight the game
    * asks of its bearer — creations and utility spells included — not
    * only direct attacks.
+   * Rev 4: "the door will relock behind you" means it — passing through
+   * an unlocked door shuts it at the walker's back unless a hand holds
+   * it; unpassed, it relocks at turn's end as before.
    */
   deckRev?: number;
 }
@@ -3950,14 +3953,24 @@ function doMove(prev: GameState, direction: Side, over = false): CommandResult {
     } else if (edge === "door" &&
         (doorIsOpen(state, key) || (displays(p, "master-key") && state.doorStates[key] !== "jammed"))) {
       // The displayed MASTER KEY turns in every lock it meets: the walker
-      // passes without another cast, and the door relocks behind them at
-      // turn's end like any picked lock. A JAMmed LOCK still refuses it.
+      // passes without another cast, and the door RELOCKS BEHIND THEM at
+      // once — "door relocks behind you" grants no lingering opening, so
+      // bystanders see only a shut door (the bearer's own threshold peek
+      // rides the key itself). A JAMmed LOCK still refuses it. To hold a
+      // door open, cast the key at it as ever.
       if (!doorIsOpen(state, key)) {
-        state.openDoorEdges.push(key);
         events.push({ type: "doorUnlocked", player: p.id, edge: parseEdgeKey(key), withCardId: "master-key" });
       }
       p.position = dest;
       via = "step";
+      // "The door will relock behind you": stepping through an unlocked
+      // door shuts it at the walker's back unless a hand holds it open.
+      // (Rev 4; earlier games kept their turn-long openings.)
+      if ((state.config.deckRev ?? 1) >= 4 &&
+          state.openDoorEdges.includes(key) && !state.heldDoors.some((h) => h.key === key)) {
+        state.openDoorEdges = state.openDoorEdges.filter((k) => k !== key);
+        events.push({ type: "doorsRelocked", count: 1 });
+      }
     } else if (edge === "firewall") {
       // "Passing through it does four points of magical damage." Firewalls
       // burn even a MIST-BODY.
diff --git a/packages/engine/test/durations-doors-cards.test.ts b/packages/engine/test/durations-doors-cards.test.ts
index 641f032..0157608 100644
--- a/packages/engine/test/durations-doors-cards.test.ts
+++ b/packages/engine/test/durations-doors-cards.test.ts
@@ -1,6 +1,6 @@
 import { describe, expect, it } from "vitest";
 import { applyCommand, activePlayer, boardView, createGame, sustainedOn, type GameState } from "../src/game";
-import { cellKey, edgeKey, neighbor, type Side } from "../src/board";
+import { cellKey, edgeKey, neighbor, opposite, type Side } from "../src/board";
 import type { CardInstance } from "../src/cards";
 import { newGame, must, giveCard, toRound2, faceOff, castAt } from "./helpers";
 
@@ -111,7 +111,7 @@ describe("doors", () => {
     throw new Error("no door on this board");
   }
 
-  it("pick lock opens an adjacent door until end of turn", () => {
+  it("pick lock opens an adjacent door — and it relocks behind the walker", () => {
     let { state } = newGame();
     const me = activePlayer(state);
     const door = findDoor(state);
@@ -130,9 +130,8 @@ describe("doors", () => {
     state = must(state, me.id, { type: "move", direction: dir });
     expect(cellKey(activePlayer(state).position)).toBe(cellKey(other));
 
-    // Relocks when the turn ends.
-    state = must(state, me.id, { type: "endTurn", draw: 0 });
-    state = must(state, activePlayer(state).id, { type: "endTurn", draw: 0 });
+    // "It will relock behind you": shut at the walker's back at once —
+    // the way back is barred without another pick.
     expect(state.openDoorEdges.length).toBe(0);
     expect(applyCommand(state, me.id, { type: "move", direction: dir === "E" ? "W" : "N" }).ok).toBe(false);
   });
@@ -539,7 +538,7 @@ describe("the displayed MASTER KEY", () => {
     }
   });
 
-  it("its bearer walks through locked doors, which relock behind them", () => {
+  it("its bearer walks through locked doors, which relock at their back", () => {
     const { state, cell, side, key, keeper } = keyRig();
     const mk = giveCard(state, keeper.id, "master-key", "MK");
     keeper.displayed.push(mk.instanceId);
@@ -548,9 +547,12 @@ describe("the displayed MASTER KEY", () => {
     if (r.ok) {
       const after = r.state.players.find((p) => p.id === keeper.id)!;
       expect(cellKey(after.position)).toBe(cellKey(neighbor(cell, side)));
-      // Unlocked for the turn — the relock rides the usual end-of-turn sweep.
-      expect(r.state.openDoorEdges).toContain(key);
+      // "Door relocks behind you": no lingering opening for bystanders.
+      expect(r.state.openDoorEdges).not.toContain(key);
       expect(r.events.some((e) => e.type === "doorUnlocked")).toBe(true);
+      // The key turns again on the way back.
+      const back = applyCommand(r.state, keeper.id, { type: "move", direction: opposite(side) });
+      expect(back.ok).toBe(true);
     }
   });