They're Playing with Fire is a 1984 American erotic thriller film directed by Howard Avedis and starring Sybil Danning, Eric Brown, Andrew Prine, and Paul Clemens.

English literature professor, Dr. Diane Stevens, works at Ocean View College, where she hires student Jay Richard to varnish her yacht 'Lillian'.

The two convince Jay to scare Michael's relatives out of the house so they can put them in a retirement home.

Later, Jay's girlfriend Cynthia, tries to blackmail him by threatening to show pictures of him and Diane on the yacht together to everyone on campus.

Jay looks around the yacht and finds a fragment of television screen glass, blood on trainers, a gun and bills for a children's psychiatric hospital in Switzerland.

Cynthia visits Michael's house to show him the photos of Diane's affair but is killed by the murderer, now dressed as Santa Claus.

There, George confronts the killer, who is called Martin and suffers from Huntington's chorea for which he is terminal.

George convinced the family to fly Martin from Switzerland so he could inherit the fortune instead of Michael and Diane.

[2] On its release, several reviews, including the Los Angeles Times and The Hollywood Reporter advised that the print advertisement was misleading as it suggested a “sex romp” opposed to a “horror-thriller.”[2]