Game Design Document: Core Mechanics
Detective Investigation Game

1. Core Philosophy

The game forces players to be observant and critical of their surroundings at all times. Every puzzle is solved through careful observation, note-taking, and logical deduction rather than inventory puzzles or pixel-hunting. Players must actively think like a detective.

2. Interaction System

• Primary interaction key: E (universal “Examine / Talk / Pick up” button).
• All interactable objects, NPCs, and clues are highlighted with a subtle glow or outline when the player’s cursor hovers over them.
• Pressing E on a highlighted object/NPC/clue triggers the appropriate action.

3. Clue & Mind System (“The Brain”)

• A Mind icon (brain silhouette) is permanently visible in the bottom-left corner of the HUD.
• Every clue collected is automatically stored in the Mind.
• A small, non-intrusive notification popup appears in the bottom-right corner whenever a new clue is added (e.g., “Clue added: Torn bus ticket – 14:32 departure”).
• Clues are text-based and can be reviewed at any time by clicking the Mind icon.

4. NPC Interaction & Interrogation

• Talking to any character uses the E key → classic dialogue box appears (styled exactly like Duck Detective: portrait on left, text on right, choice wheel at bottom).
• Unknown characters appear as “???” until their name is learned.
• Interrogation system:
  • Click any clue in the Mind while talking to an NPC → the detective automatically asks a question based on that clue.
  • NPCs can give new clues in their answers.
  • If an NPC says something that contradicts a previously known clue, the contradicting clue in the Mind lights up with a red exclamation mark. Clicking it lets the player confront the NPC about the contradiction.
• Example dialogue flow:
  NPC: “I was at the office all evening.”
  (Player notices contradiction with “Bus ticket 14:32”)
  → Player clicks the bus ticket clue → Detective: “Funny, because this ticket says you left at 14:32…”
• Some NPCs are not sure of some things.. adds "I think" at the end.
• Some NPCs maybe have to be bribed with some item or money to reveal info.

5. Inspection Mechanics (Press I)

• People: Press I on any NPC to enter “Close Inspection” mode.
  • Reveals detailed appearance notes automatically added to the Mind (e.g., “Gold wedding ring on left hand – engraved ‘A & M 2019’”).
  • Some NPCs have small items on their body that become separate clues (watch, keychain, stain on sleeve, etc.).
• Large or cluttered objects: Press I to zoom in and scan (e.g., messy desk, car interior, bulletin board).

6. HUD & Menu System

Bottom bar (always visible):

• Mind icon (left) → opens Deductions and Suspects tabs
• Inventory icon (middle) → collected physical evidence/items
• Map icon (right)

Tabs inside Mind menu:

• Deductions (main puzzle screen):
  Fill-in-the-blank style deduction board.
  Example:
  “The killer is ___ and used ___ as the weapon because ___.”
  Player drags collected clues from the sidebar into the blanks.
  Basically any combination of the collected clues are possible, but only the logically correct one advances the case (prevents brute-forcing).
• Suspects tab:
  Profiles of every examined person with their appearance details and known facts.
• Closed tab:
  Automatically appears after a case is solved. Contains a summary of the solved case with all correct deductions. Clues associated with the case are also removed.

7. Tutorial & Onboarding

The game begins with a very simple personal investigation (exactly like the opening of Duck Detective):
The player (as the detective) investigates their own messy apartment/office to find their lost keys.
This teaches:

• E to interact
• I to inspect
• Collecting first clues
• Opening the Mind menu
• Simple deduction board

8. Player Guidance Dialogues

The detective (player character) speaks in first-person inner monologue to gently guide the player without breaking immersion.
Examples:

• “Well, thankfully, I remembered to take that piece of paper before leaving the scene…”
• “First I need to investigate the car. Something about those tire tracks doesn’t add up.”
• “I should probably talk to the security guard again… that alibi feels off.”

9. Special Mechanics – Password Cracking

Certain levels feature a laptop or locked computer that requires password cracking as a mini-game:

• Player must combine clues from the environment and interrogations to guess the password.
• Example: Clues collected → “Wife’s name: Maria”, “Dog: Max1998”, “Favorite band: Queen”
• Player types possible passwords; correct combination unlocks files that contain new clues or evidence.
• Failure states are forgiving (no game over, just “Access Denied” and hint to gather more clues).

Summary of Core Loop

1. Explore environment → use E and I to find clues.
2. Talk to NPCs with E and interrogate using collected clues.
3. Review clues in Mind → build Deductions.
4. Solve deduction board → confront final suspect → case closed.

This structure keeps the game intuitive, fair, and highly replayable while rewarding sharp observation and logical thinking.