Continuity mistake: When Billy and Brenda are arguing in her apartment towards the start of the episode, the pendant on Brenda's necklace moves itself back and forth between shots.
Continuity mistake: When Brenda and Billy are arguing in the casino, the shoulder strap of Brenda's handbag moves from tucked under her collar in the close ups, to sitting halfway along her shoulder in the long shots.
Chosen answer: It is strongly implied that Lisa was murdered by her brother-in-law Hoyt, with whom she had been having an affair. When Nate confronts Hoyt about Lisa's disappearance, Hoyt shoots himself dead before the question is finally resolved.
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