Stana Katic, Nathan Fillion

We know Richard Castle will do anything for his partner/muse/lover Detective Beckett. But on Monday's episode of Castle (10/9c, ABC), that might (literally) cost him a lot.

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The Storage Wars-inspired episode, titled "Secret's Safe with Me," finds Castle (Nathan Fillion) and Beckett (Stana Katic) looking into the auction of a storage unit that may be connected to a woman's murder. There's just one problem: Beckett doesn't have enough time to get a warrant, so the only way to protect what may be key evidence is for Castle to join in on the bidding!

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But as you can see in our exclusive sneak peek video below, that unit full of junk may be much more valuable than Castle realizes — and certainly worth more than what he has in his wallet! Watch below to see if Castle can win the auction for Beckett. Plus: Why does Castle carry so much cash with him in the first place?

Castle airs Mondays at 10/9c on ABC.