Simon Baker, Aunjanue Ellis

Who set fire to serial cop-killer Todd Johnson, executing him in his jail cell? That mystery has been haunting the characters on The Mentalist since November, and tonight one of the CBI's very own is fingered as the perp!

First, Agent J.J. LaRoche (Pruitt Taylor Vince), who's been investigating the case as head of CBI's internal affairs, will reveal that one of Johnson's victims had been sleeping with Madeleine Hightower, the CBI boss played by Aunjanue Ellis. Then LaRoche drops an even bigger bombshell: Hightower was the only one with both a clear motive and security clearance to enter Johnson's cell. Soon after, Hightower holds Patrick Jane (Simon Baker) hostage with a gun to his head and makes an escape from CBI headquarters.

"It's a real shocker," says Ellis. "Since I'm not a series regular, I've never assumed anything, especially because the writers have given Hightower this impenetrable veneer of mystery."

The episode also delivers more mind-bending hints about supervillain Red John and his growing network of associates — and it's driving the cast crazy. "The actors all sit around asking each other, 'Who do you think Red John is?'" says Ellis. "After a while, you start thinking, 'Is it me?' You can't help but get a little paranoid, because The Mentalist is that kind of show!"

The Mentalist airs Thursdays at 10/9c on CBS.

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