Jill Brewer (Frances Tomelty) is the hidden main villainess from "Home Truths," the penultimate episode of New Tricks' first season (airdate 29 April 2004). She is the wife of Rick Brewer and a friend of Donna Adamson, who--along with her infant son, William--went missing in the summer of 1971.
UCOS was on the case of Donna's disappearance, with Donna being revealed as having passed on, and throughout the episode, it was led to believe that Jill was one of three women who were abducted by an attempted serial killer, with Donna and Kay Grant as the other two. However, the episode's climax revealed that not only Jill was alive, but she was actually a kidnapper, as she abducted baby William. Jill's backstory revealed that she suffered a miscarriage and wasn't permitted from adopting, and on that summer day in 1971, Jill paid Donna a visit, and the three of them (including baby William, who was in a carriage) went to Willow Ponds, where Donna suddenly removed all of her clothes and jumped in the water.
After doing so, Donna was struggling for safety, with Jill thinking that Donna was joking, only realizing too late that she was in trouble. Donna tragically drowned, but instead of calling for help, Jill abducted William, using Donna's tragic and sudden death to have a baby of her own. As part of the ruse, the evil Jill claimed that William's father was Black (as William was bi-racial) and had died, while also moving to Ireland and marrying into money--while also still married to Rick.
Jill was found by Brian Lane and Jack Halford, where she was revealed as being terminally ill and dying. When asked about Donna and William, Jill confessed to the abduction, doing so only due to the fact that she had months left to live. She stated that Donna's death was an accident, though she also said that Donna's death was God's way of giving her a second chance at motherhood. The villainess also expressed pride in her actions and that she was a good mother to William, though she revealed that they were estranged after William left home at age 16. Jill was arrested (off-screen), but not before revealing the location of Donna's body.