Chekhov's Missing Gun

Chekhov appears at my writing desk: "If there's a gun in act one—"

Me: "I know, I know. It has to fire in act three."

Chekhov: "No, no. I lost my gun. Have you seen it? Small revolver, mother-of-pearl handle."

Me: "...What?"

Chekhov, searching my drawers: "I've been looking for three acts now."