Castle already has to solve the mystery of Beckett's sudden disappearance and why a team of mercenaries are chasing her. But apparently, the show wants even more puzzles to solve!

The conclusion to the two-part season-opener (Monday at 10/9c, ABC), will explain what happened to Beckett (Stana Katic), filling in the gaps from the previous episode, which took place entirely from Castle's perspective. And as you can see in the exclusive sneak peek above, whatever Beckett and her new pal Vikram (Sunkrish Bala) are up to, it's plenty dangerous.

How much life is left in Castle?

Although Beckett takes a shot to the gut when the mercenaries track her down, just when it looks like Beckett's at the end of the road, a mysterious woman (guest star Ann Cusack) steps in to save the day. Although she initially refuses to answer any questions about her identity (after all, they probably should focus on escaping!), Beckett finally wears her down."You can call me Rita," she says matter-of-factly. "I'm Castle's stepmother."

What?! Who is she and how is she mixed up in all of this? Watch the clip above and check out Castle on Monday at 10/9c on ABC.