Buckle your seat belts, folks, it's going to be a bumpy ride! Tonight Castle airs the first of a two-part arc that will shake the team to its very core, though at the outset there's nothing to distinguish this case from any of the other missing cases they've worked on over the past five years.

The episode begins in an alley with a gunman, viciously run down by the van he's aiming his gun at. Castle (Nathan Fillion) and Beckett (Stana Katic) arrive at the scene the next morning discussing Castle's heroic attempts to allow his college-aged daughter to fly from the nest without checking up on her every five minutes.

Beckett questions whether it's acceptance or denial that's bringing all of his feelings to the surface, but before he can think too deeply about his answer, their attention is turned to the now very dead gunman.

As the investigation gets rolling, it appears that the victim, Hasim Farouk, is involved in illegal activities. His gun, found at the scene, has a custom-made grip, and his posh apartment yields a personal arsenal of weapons along with surveillance equipment. Beckett also discovers monthly $25,000 payments being made to a Swiss bank account. The word "terrorist" is bandied about, making Castle more than a little nervous as the man was enrolled in the same college as Alexis (Molly C. Quinn), but he's determined not to panic and call to check in on her, even when they make a visit to the campus.

Castle season 5 episode 15 FBI Gates

Before long, video footage is unearthed showing a girl being grabbed and shoved into the same van Hasim was shooting at. The girl's name is Sara El-Masri (Karen David) and her father is a wealthy Egyptian man who's made plenty of enemies back home. Anwar El-Masri (Bernard White) and his wife Lina (Katherine Kamhi) inform them that they hired Hasim to protect their daughter when she refused to be escorted by a proper bodyguard. The FBI is brought in to investigate the kidnapping, while Castle and Beckett remain on the murder case.

The pair's next stop is at a science lecture Sara attended just before her abduction, which is located near to where Hasim's body was found. But there is one tidbit of information they pick up which turns the case on its ear: Alexis was with Sara at the lecture and her phone was recovered on the street just outside the building.

From this point on, Fillion does a great job of portraying a dad in a helpless tailspin, reaching the pinnacle when he "appeals" to the van driver to get the information he needs. Though Gates (Penny Johnson) gives full backing to the team's efforts to recover Alexis, she and the FBI point man Harris (Dylan Walsh) send Castle home to wait for a potential ransom call.

Castle season 5 episode 15 Beckett Castle

Through it all, Kate becomes Castle's rock, anchoring him with the assurances that they are doing everything they can and reminding him that they always come through in the end. There's a great scene between the two when Castle thinks it might be Alexis' blood in the back of a van. The scene between them near the end is also very poignant, shedding a ray of hope into the darkness.

For her part, Molly C. Quinn plays a good abductee. Her scenes deliver the right amount of determination and tension and keep the audience on edge to the very end. The lock-picking scene is especially well-played, as are the moments where she finally gets in touch with her dad.

Whether Alexis' decision to have the girls split up will backfire on her next week or not remains to be seen, but if it's anything like this one, next week's conclusion will keep audiences riding on the edge of their seats until the final credits roll.

Castle airs @10pm on ABC.