Curious about the high mortality rate among Mooseville's carpenter class, Qwill starts to suspect foul play.

Shortly before Qwill arrives, Buddy Yarrow, a carpenter, drowns while fishing, but the police report it as an accident.

When he arrives, Qwill discovers his heater is broken, so calls a nearby resident and friend, Mildred Hanstable.

He decides to build an addition to his cabin but is advised against it, because during the summer, all the good contractors are busy with big jobs, so the people are forced to hire itinerant carpenters, or Underground Builders as they are referred to by the locals, who are unreliable.

But Qwilleran is lucky and finds out that Clem Cottle, a reliable and experienced carpenter, needs money and so could work for Qwill.

After a squall hits, the men become stranded on the island and are later rescued after a harrowing experience and taken to the Pickax hospital.

He is released the next day and arrives home to find Iggy's truck is parked in the drive, but the carpenter is nowhere to be found.

Qwilleran rides out to her house to give her the papers but finds it flooded by the rain that came with the storm that marooned Qwill on the island.

Qwilleran lets the cat down and he leads them to a list of names of carpenters who had died recently, written in the lipstick used by Little Joe.

He then confronts her with the murder of her father, which she had rigged so it appeared to be an accident; Buddy Yarrow, who was fishing on her property; Mert, another underground builder who went missing and was never seen again; Clem Cottle; and Iggy, whose real name is Ignatius K. Small.