Cleo Jennings, aka Tammy Ann Lacoss (Jenny Wade), is the main villainess from "Black is the Widow," episode 1.17 of Magnum P.I. (airdate March 4, 2019). She was introduced as a woman who once dated wealthy Roland McDowell, the episode's murder victim.
As revealed, however, Cleo was actually a con artist, and her real name was Tammy Ann Lacoss. She was also the lover of carjacker Davis Sadler, and they had bilked five victims out of money before Cleo/Tammy's date with Roland. The plan was to rob Roland of $1 million, with the villainous couple using Roland's daughter, Karen, as a bargaining chip. Under the threat of harm to Karen, Roland took the money out of his account, after which Cleo shot him to death, making the murder look like a carjacking.
Karen went to Thomas Magnum regarding her widowed father's murder, and after Roland's dating history was uncovered, Magnum went undercover as Dr. Tomas Caballe and dated each of the women. Among the women was Cleo, who expressed shock over Roland's murder and took on a peppy persona to mask her role. Another woman, Abby Miller, ended up suspected when Magnum spotted her with a man fitting the description, but she was cleared when Abby (who found out Magnum's true identity) confronted him and stated that she had an alibi--all the while, Cleo visited Magnum and returned his cell phone to him.
TC and Rick's investigation of the stolen car ended up revealing Sadler as the thief and Cleo as the main culprit and killer, leading to Detective Katsumoto arriving at the villains' home and handcuffing her to her car while pursuing Sadler. However, after being informed that Katsumoto was missing, it was revealed Magnum's phone wasn't lost--Cleo took it and copied his SIM card, allowing her and Sadler to track his calls. As for Katsumoto, the couple held him at gunpoint and forced him to help them escape, but after Rick fired a shot at Sadler, Katsumoto was able to hold Sadler captive. Meanwhile, the evil Cleo attempted to escape in her car, but she was trapped by both Magnum and Juliet Higgins, after which Cleo and Sadler were both arrested.