After a faked death last week, Body of Proof visits a mental hospital this time around, perpetuating the idea that there's no such thing as a garden-variety murder in TV's Philadelphia. There's normally nothing wrong with that, but this particular demise is more like a movie of the week.

A young woman named Renee is found dead in the shower of a psychiatric institution for girls, bringing Megan, Tommy and Tommy's would-be girlfriend Riley Dunn (guest star Marisa Ramirez) to the scene. Megan can tell Riley has a thing for Tommy, who must be over his all-of one-episode-interest in Riley, because he tells Megan that he's "saving myself for someone special." As quickly as the possible love triangle arrived, so has it departed.

Returning to the murder, the hospital's director is Dr. Derek Malcolm (guest star Craig Bierko, who previously played a romantic rival to Mark Valley's Brad Chase on Boston Legal), and he's the usual authority figure who doesn't want to help the investigation. Another patient named Darby tells Tommy that she saw a man sneaking around the hospital, and also believes that she, not Renee, was the person he wanted to kill. Cue Megan seeing Dr. Malcolm looking on ominously. Tommy's skeptical, but Megan persuades him to investigate the young woman's statements anyway, as if he wouldn't already do so given that it's his job.

She then meets with her mother (guest star Joanna Cassidy), telling her about the unidentified fingerprint found on her father's suicide note, and asking to exhume the body. Mom Hunt is still not pleased with Megan's digging into the past and refuses to provide the necessary signature. The next day, Megan calls in Dr. Charlie Stafford (a returning Luke Perry from "Skin and Bones"), in order to go around her mother. He agrees to see what he can do.

In the lab, Curtis wonders how someone inside a mental hospital got access to a ball peen hammer, which may be the murder weapon. Megan is pulled away from the autopsy to meet with Tommy and Mo Childs (guest star Jude Ciccollella, 24), the detective who investigated the earlier murder of Darby's sister, Beth. Childs tells them everything he knows about Beth's still-unsolved case, and asks if they believe there's a connection between the two. Tommy isn't sure yet, but the conversation is enough to send him and Megan back to the hospital to ask Dr. Malcolm for permission to interview Darby. This would be a good idea if Darby wasn't drugged, which sets Megan off on another rant.

One of the CSU technicians tells Tommy that they've inspected the heating vent and confirmed that someone's definitely come through it, which confirms Darby's story. Once she's alert enough to talk to them, the young woman says that her mother hired the mysterious man to kill her - because she saw her mother murder her sister and then her mother made her lie about it to the cops. Take a second to wrap your brain around that. "That's why she sent me here. To shut me up," Darby continues, going on to insist that her mother pays Dr. Malcolm to keep her quiet, and asking for Tommy and Megan's help.

Shifting gears, Megan awkwardly runs into Riley in the bathroom, with Riley wanting to know if something is going on between Megan and Tommy. "It's none of your business," Megan rightly responds. Riley tells Megan that she did go on that previously mentioned date with Tommy to the Flyers game and just wants to know what to do. Megan tells her, "You do whatever you want."

She and Tommy then interview Darby's mother (guest star Sharon Lawrence), by which we mean Megan pokes and prods while Tommy essentially holds down the furniture. The only thing he points out is that she did donate money to the hospital. Darby's mom lets slip that she told Dr. Malcolm that he could start electroshock therapy. That sends Megan straight back to Dr. Malcolm, feathers ruffled and insisting that she's going to put a stop to things. She doesn't need to - Darby attacks Dr. Malcolm and escapes from the hospital, after which the doctor holds Megan responsible.

Megan's shocked to get a call from Lacey, who tells that Darby has shown up at their apartment. When Megan and Tommy get there, her daughter and the mental patient are playing Scrabble. While Darby gets ready to leave, Megan confesses to Tommy that she sees herself in the young woman. They take her back to the police station and ask her what she remembers about her sister's murder, and Darby tells them enough for them to obtain a search warrant for her mother's home, where Megan finds the necklace Darby's mother was allegedly wearing the night she murdered Beth. It goes back to the lab, where Ethan finds human blood on it that matches Beth.