Bones' key couple may have a second baby on the way, but their marriage is headed for less happier times.

As we previously reported, Booth (David Boreanaz) will once again face his former gambling addiction later this season. "There is a murder that involves an underground poker game, and it appears as if Booth is the only logical person to go undercover," executive producer Stephen Nathan tells TVGuide.com. "He assures everyone that he's got his act together, but he is tested in a way that surprises even him. Booth is forced to confront some very old demons that he thought he had rid himself of."

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Nathan teases that Booth's problem will be so serious that his relationship with Brennan (Emily Deschanel) will be in major jeopardy. "We see Booth and Brennan going through a torturous situation for their relationship," Nathan says. "The relapse has very far-reaching effects. It weighs on both of them, and affects their marriage in a very fundamental way. Things will happen that we never thought could happen to Booth and Brennan." Yikes!

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