Mary Ann Eagin (Marina Sirtis) is the main villainess from Diagnosis Murder episode 5.20, "Murder at the Finish Line" (airdate March 26, 1998). She is the owner of Eagin Racing, but she was revealed to be having financial problems. She used the money raised for her team to cover her losses, but she oversold her shares to various investors.
Once Matt Thomas started winning numerous races, Mary Ann resorted to villainous methods to keep the investors from wanting a return on her money. She poisoned Matt hours before his race, and to make sure he would be killed, she sabotaged the engine in his car, leading to his crash. The team was able to get a new engine working, but later that evening, the evil Mary Ann snuck into the garage and sabotaged the engine, doing so by pouring an explosive substance inside.
Mary Ann was revealed as the villainess when she ducked for cover while the engine was being tested, something Mark and Steve Sloan counted on. Mary Ann was arrested for her crimes, and she was left incredulous over how Matt was winning so much.
- Marina Sirtis also played the villainous Detective Inspector Walker in the 1996 film, Gadgetman, as well as Layla Mokhtari from the TV series The Closer.
- She is also best known for voicing villainess Demona on Gargoyles.