The Black Files · October 14, 2026 · Difficulty: Senior Detective
Black File #125 — SolutionLights Out
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The case
Eric Chandler, health inspector, was found dead at Marlow's Restaurant at 12:50 AM. Seven people were at the scene. Exactly one of them was alone with Eric in the same zone.
The evidence (10 clues)
- Adrian was standing on stairs.
- Derek was in the Back Alley.
- Frank was in the Bar.
- Beth was standing on the floor.
- Adrian was in the Dining Room.
- Frank was sitting in a chair.
- Carla was standing on stairs.
- Graham was the easternmost person at the scene.
- Frank was the northernmost person at the scene.
- Carla was the southernmost person at the scene.
The answer
The killer: Carla Trask, alone with Eric Chandler in the Kitchen.
Nothing is forced until you test Graham at G2 or G6: every wrong cell breaks the two-people rule in the victim's zone. With Graham at G2 the rest cascades and leaves Carla alone with Eric in the Kitchen.
Step-by-step deduction
- Before placing anyone, each clue eliminates cells:
- • Carla: was on the stairs; was the southernmost person of all, and since there is one person per row somebody occupies row 7: that is Carla. Only E7 is left.
- • Derek: was in the Back Alley; row 7 already belongs to Carla; column E already belongs to Carla; column D already belongs to Frank; column G belongs to Graham. Only F5 is left.
- • Frank: was in the Bar; was sitting in a chair; was the northernmost person of all, and since there is one person per row somebody occupies row 1: that is Frank. Only D1 is left.
- • Adrian: was on the stairs; was in the Dining Room. Remaining: A2 and A3.
- • Graham: was the easternmost person of all, and since there is one person per column somebody occupies column G: that is Graham; row 7 already belongs to Carla; row 1 already belongs to Frank; row 5 already belongs to Derek. Remaining: G2 and G6.
- • Beth: was standing on the floor; row 7 already belongs to Carla; column E already belongs to Carla; row 1 already belongs to Frank; column A belongs to Adrian; column G belongs to Graham; row 5 already belongs to Derek; column F already belongs to Derek. Remaining: B2, C4 and C6.
- • Eric: row 7 already belongs to Carla; column E already belongs to Carla; row 1 already belongs to Frank; column D already belongs to Frank; column A belongs to Adrian; column G belongs to Graham; row 5 already belongs to Derek; column F already belongs to Derek. Remaining: B2, C2, B3, C3, C4, B6 and C6.
- That already places Carla at E7, Frank at D1 and Derek at F5.
- At this point no cell is forced. Time to test a hypothesis. Try Graham, who can only be at G2 or G6.
- – Graham at G2: everything fits: it yields Adrian at A3, Beth at C4 and Eric at B6.
- – Graham at G6: Adrian, Beth and Eric would all be in the Dining Room: the victim cannot have more than one companion. Impossible.
- So Adrian goes to A3, Graham goes to G2, Beth goes to C4 and Eric goes to B6.
- With all seven placed, the only people in the Kitchen are Eric and Carla: Carla was alone with the victim.
