Gladys Mitchell (Maureen Thomas) is the main villainess from Psych episode 2.10, "Gus' Dad May Have Killed an Old Guy" (airdate December 7, 2007). She is the wife of Carl Mitchell, the head of the homeowner's association and the descendant of the founders of their neighborhood.
However, 30 years prior, Gladys was having an affair with a widower who she visited frequently; an affair that began when Gladys delivered flowers to him. Her illicit tryst was witnessed by Old Man Fuller (a grouchy curmudgeon who had dirt on all of his neighbors), and she ended up being blackmailed by him. Since then, Gladys was forced to cater to Fuller's demands, which she was willing to do because she was hoping he would die someday. Not only did Fuller continue to live, he went senile, and with the fear that Fuller could reveal Gladys' secret out of the blue, the villainess decided to kill him.
First, Gladys poisoned his tea, but Fuller spit it out (staining his shirt and breaking the cup). She later bashed his head with a hammer, but that only dazed him. Finally, the evil Gladys tied a rope around Fuller's neck and tied the other end to a chair lift, and later sent the lift down--hoisting Fuller from the ground and choking him to death. The death appeared to look like a suicide, but Shawn and Gus deduced it was murder early in the episode. Gladys' reveal came when Gus pinpointed that she was wearing Gardenia perfume, the same scent she had during the affair. Gladys stated to her husband that she couldn't let Fuller ruin everything they worked so hard to build, right before she was handcuffed and arrested by Juliet.