Written by Derek Ford and Alan Birkinshaw, the film follows a mysterious killer murdering Santa Claus impersonators in London during Christmastime.

At Scotland Yard, Chief Inspector Ian Harris and Detective Sergeant Powell discuss the murders, and interview Kate, and her boyfriend Cliff.

The next day, a present (which reads "Don't Open Till Christmas") is delivered to Harris, Powell receives a strange call from a man claiming to be a reporter named Giles, and a Santa is shot in the mouth.

A Santa is chased into a theatre where Caroline Munro is performing, and his body is brought to the stage by a trapdoor after he is stabbed in the face with a machete.

Kate tells Powell of her suspicions about Harris (who has no birth certificate) but he dismisses her theories, so she goes to visit Parklands alone, while the killer castrates a Santa in a department store restroom.

A flashback is then shown, and reveals that decades earlier Giles walked in on his father (who was dressed as Santa for a Christmas party) cheating on his mother with another woman.

Harris wakes up from a nightmare, goes into his living room, and unwraps the gift he had gotten earlier, which has a previously unseen card that reads "Christmas present from your loving Brother".

[2] Alan Lake, who portrays Giles Harrison, committed suicide shortly before the film was released in the wake of the death of his wife Diana Dors earlier in 1984.

[5] DVD Verdict called the film "barely watchable", concluding "there's very little redeemable about Don't Open Till Christmas, but for exploitation die-hards, Dick Randall's productions are always worth watching for a lot of blood, sex, and a few laughs".