Nightmares & Dreamscapes: From the Stories of Stephen King (2006)

S1E12 Lady in Question

Johnny McKay's former flame arrives in town, bringing along her current boyfriend, who taunts Johnny into a duel. In the confrontation, Johnny ends up killing him, but when he returns with Dan Troop, the man's gun is nowhere to be found. As a result, Troop has no choice but to arrest Johnny for murder.