Sleuthic

The Black Files · October 2, 2026 · Difficulty: Investigator

Black File #113 — SolutionThe Fuel Line

Missed the case? Play Black File #113 →

The case

Gail Farrell, charter captain, was found dead at Harbor Point Marina at 12:50 AM. Seven people were at the scene. Exactly one of them was alone with Gail in the same zone.

The evidence (8 clues)
  1. Elliot was sitting on the sofa.
  2. Byron was in Dock A.
  3. Curtis was in the Harbormaster's Shed.
  4. Daniel was sitting on the sofa.
  5. Elliot was in the Harbormaster's Shed.
  6. Felicia was the westernmost person at the scene.
  7. Alvin was the northernmost person at the scene.
  8. Curtis was the southernmost person at the scene.

The answer

The killer: Daniel Nakamura, alone with Gail Farrell in the Boat Yard.

Fixing rows and columns from the extreme-position clues cascades through the board and leaves Daniel alone with Gail in the Boat Yard.

Step-by-step deduction

  1. Before placing anyone, each clue eliminates cells:
  2. • Alvin: was the northernmost person of all, and since there is one person per row somebody occupies row 1: that is Alvin; column A belongs to Felicia; column B already belongs to Byron; column G belongs to Elliot; nobody else can occupy column E, so it must be Alvin. Only E1 is left.
  3. • Byron: was in Dock A; row 1 belongs to Alvin; column A belongs to Felicia. Only B2 is left.
  4. • Curtis: was in the Harbormaster's Shed; was the southernmost person of all, and since there is one person per row somebody occupies row 7: that is Curtis; column G belongs to Elliot. Only F7 is left.
  5. • Daniel: was sitting on the sofa; row 1 belongs to Alvin; row 7 belongs to Curtis; column A belongs to Felicia; nobody else can occupy column D, so it must be Daniel. Only D5 is left.
  6. • Elliot: was sitting on the sofa; was in the Harbormaster's Shed; row 5 already belongs to Daniel. Only G3 is left.
  7. • Felicia: was the westernmost person of all, and since there is one person per column somebody occupies column A: that is Felicia; row 1 belongs to Alvin; row 2 belongs to Byron; row 7 belongs to Curtis; nobody else can occupy row 4, so it must be Felicia. Only A4 is left.
  8. • Gail: Gail cannot be in Dock A: the crime zone holds exactly two people and Alvin and Byron are already there, and with Gail that would be more than two; Gail cannot be in the Harbormaster's Shed: the crime zone holds exactly two people and Curtis and Elliot are already there, and with Gail that would be more than two; row 2 belongs to Byron; row 7 belongs to Curtis; column A belongs to Felicia; nobody else can occupy row 6, so it must be Gail; nobody else can occupy column C, so it must be Gail. Only C6 is left.
  9. That already places Byron at B2, Daniel at D5, Felicia at A4, Gail at C6, Alvin at E1, Curtis at F7 and Elliot at G3.
  10. With all seven placed, the only people in the Boat Yard are Gail and Daniel: Daniel was alone with the victim.
Solved map of Black File #113: Alvin E1, Byron B2, Curtis F7, Daniel D5, Elliot G3, Felicia A4, Gail C6
The solved map: Alvin E1, Byron B2, Curtis F7, Daniel D5, Elliot G3, Felicia A4, Gail C6.

Play today's case →