Contains spoilers for this episode and earlier episodes.
Soos discovers a forgotten room containing Stan's collection of wax celebrities. After one figure melts, Mabel uses the leftover wax to sculpt a lifelike replacement of her great uncle. Stan becomes attached to his double and reopens the wax museum as a Shack attraction. When the new statue loses its head, he treats the damage as a murder. Dipper and Mabel volunteer to investigate, confident that their detective skills can succeed where the local police seem uninterested. An axe and unusual footprints lead them toward townspeople who might have a grudge against Stan, beginning with the angry lumberjack Manly Dan.
The twins discover that their weapon belongs to a left-handed attacker, which rules Dan out. They accuse reporter Toby Determined next, but an embarrassing recording supplies his alibi. At the memorial for Wax Stan, Dipper finally connects the holes in the footprints with the display stands beneath the figures' shoes. The wax celebrities themselves committed the attack. Cursed to move when the moon waxes, they wanted revenge for years of being shut away and mistook Mabel's sculpture for the real Stan. Dipper and Mabel fight them with heat, and Dipper leads Wax Sherlock Holmes into sunlight. With the attackers defeated, the twins recover the missing head and give Stan back his cherished double.