Case file Crossclimb Level 12: 4-letter ladder, 5 middle exhibits, combo prompt "Smoky outdoor gathering spot". Endpoints: FIRE (top) and PARK (bottom).
Middle phase answers: "Solid and unyielding" = FIRM; "Shape or structure" = FORM; "Military base" = FORT; "Harbor city" = PORT; "Section of a play" = PART.
Ordering phase: the valid middle chain is FIRM → FORM → FORT → PORT → PART. This permutation is the only valid one-letter chain for these answers.
Evidence link: FIRE → FIRM. E→M at the fourth letter (FIRE → FIRM).
Evidence link: FIRM → FORM. I→O at the second letter (FIRM → FORM).
Evidence link: FORM → FORT. M→T at the fourth letter (FORM → FORT).
Evidence link: FORT → PORT. F→P at the first letter (FORT → PORT).
Evidence link: PORT → PART. O→A at the second letter (PORT → PART).
Evidence link: PART → PARK. T→K at the fourth letter (PART → PARK).
Verdict: FIRE → FIRM → FORM → FORT → PORT → PART → PARK satisfies every one-letter constraint. The combo clue "Smoky outdoor gathering spot" describes both end words together — "FIRE" and "PARK" each differ by one letter from their adjacent middle rungs and satisfy the shared top+bottom prompt.