Goofs

When arriving at the manor, Jillian is wearing a choker when she gets out of the car, but in the next scene, her choker is gone.

When Derek is killed, everyone comes up to his corpse. In the flashback everyone (except Diane) walks up to Derek's corpse, and Diane walks in about 1 second later.

In the syndicated print of Part 2, Diane refers to hiding Lois' death by saying "...you know unless a local cat does something funny." Ironically, the cat she refers to (voiced by Patrick Stewart) appears in a scene that the syndicated print of Part 1 deleted, due to time compressing.

The gun shown in the china cabinet is black and has a suppressor. In the flashback narrated by Diane, the gun she's hiding in Tom Tucker's suite case is silver/nickel and doesn't have a suppressor attached. However, the gun Diane is holding on Lois is nickel-plated.

It was never revealed why Carl was invited.

A show is not required to provide the audience details for every aspect one might wish to know. However, as Carl punches Chris into the bookcase while all the characters are accusing others of having reason to want James Woods dead, revealing the hidden door, it can be inferred that Chris knew the reason Carl was invited.

During the atmospheric and heavy thunderstorm, the owner of the convertible parked with other vehicles outside the house fails to raise its roof.

It can be presumed that the owner of the convertible is too preoccupied with the murders in the house to think about the top being down during a storm.

Peter accidentally knocks Joe out unconscious in one scene, but when everyone is arguing with each other, Joe can be seen behind the couch arguing with Dr. Hartman.