Nathan Fillion, Kristin Lehman

Think Castle only has eyes for Beckett? Think again.

Castle has just booked The Killing's Kristin Lehman as the latest obstacle between the would-be lovers, TVGuide.com has learned. 

Fall Preview: Get scoop on all your favorite returning shows

Lehman plays Martina Kaye, a sexy art insurance investigator who joins Castle (Nathan Fillion) and Beckett (Stana Katic) on a murder investigation that involves the theft of a valuable sculpture.

As we previously reported, when Martina meets Castle, the attraction is instant, which no doubt will make for an awkward working relationship with Beckett. But Caskett 'shippers shouldn't worry too much: We hear this particular vixen also hides a surprising secret from the team.

Exclusive: Castle gets a Mr. Freeze in William Atherton

Lehman was most recently seen on AMC's The Killing as Gwen, the campaign manager (and lover) of City Councilman Darren Richmond (Billy Campbell). Her other credits include roles on Felicity, Judging Amy, Human Target and Fox's short-lived Drive, on which Fillion also starred.

Castle returns Monday, Sept. 19 at 10/9c on ABC.