Enid Is Sleeping (1990)

Harry (Judge Reinhold) is married to a woman named Enid (Maureen Mueller) but is cheating on her with her own younger sister Jane (Elizabeth Perkins). When Enid comes home she discovers them and tries to kill Harry, but Jane hits her on the head and kills her. Floyd (Jeffrey Jones), Harry's partner on the local police force, constantly meddles. It's just a matter of time before someone finds out about the unintentional crime.