It wouldn’t be a new season of “Castle” without a deadly mystery! While the Season 7 premiere last year kicked off with Rick Castle (Nathan Fillion) missing in action, episode 1 of Season 8 began with Kate Beckett (Stana Katic) on the run … and involved in a fatal shooting.

The Season 8 premiere of the ABC drama, titled “XY,” began with a man at a nightclub confronting an attractive woman about following him throughout the day. The woman admits that she had been following him … and proceeds to stab him in the stomach.

Cut to Castle and Beckett at their apartment. Beckett accepted the job as captain and Castle celebrates by getting her a cake. But it’s what’s inside the cake that is his wife’s real congratulatory gift. She reaches inside the cake to pull out a diamond bracelet engraved with the word “always.”

The two are interrupted by a phone call, which Beckett claims is from a telemarketer. However, she doesn’t have time to sit and celebrate with Castle. She heads off to a meeting, while her husband leaves to go to his newly renovated private investigator office.

Although Castle’s business venture is new, it’s already booming -- thanks to his daughter Alexis (Molly C. Quinn). Despite being a college student, she’s already solving cases for her dad (and getting college credit for it, of course). He’s a little bent out of shape about her closing more cases than him, but Esposito (Jon Huertas) and Ryan (Seamus Dever) are investigating a murder and invite him along when they can’t get in touch with Beckett.

The murder -- a shooting -- took place at an abandoned theater. Three men -- all of whom had fake IDs -- were killed by an unknown shooter in the balcony. Further investigation of the balcony reveals the bullet shells … and a pool of blood. But it’s what is hidden in the pool of blood that is the real shocker -- Beckett’s new bracelet.

Tests prove that the blood is a match to Beckett’s. Why was she there? Why did she shoot the men? And where is she now? Castle and Beckett’s co-workers have so many questions, but have limited information. Castle’s theory? Associates of the dead men must have kidnapped an injured Beckett.

Things become more suspicious when it’s revealed that she lied to her husband about having a meeting. However, Esposito and Ryan catch a break when they get an address for one of the dead men. Castle accompanies Esposito and Ryan to the apartment and have a run-in with a mysterious woman hiding behind the curtains. She manages to knock Castle down, but is stopped when Esposito and Ryan pull a gun on her.

Back at the precinct, she reveals that her name is Hayley Shipton (Toks Olagundoye). Although she’s not very cooperative, she comes clean about why she was at the apartment. She’s not an accomplice of the men, but instead a freelance security specialist who has been hired to find the person responsible for stealing Social Security numbers. Hayley's able to tell the police that there were four men and one women linked to the stolen identities, which helps Castle narrow his search for Beckett down to one woman and one man because three others are already dead.

Hayley might not have been much help, but a stolen van with blood leads the group to a local dry cleaners. A worker is able to identify Beckett, however the twist is that Beckett wasn't a hostage. Instead, Beckett told a man she was with to lock the dry cleaner worker in a restroom while she sewed up her wound. 

They don't have a photo of Beckett's accomplice, but the worker was able to reveal that he was an Indian man in his late 20s with a beard. She added that he was dizzy and had a headache. According to the woman, Beckett told the man that he should have had breakfast that morning instead of calling her, leading Castle to believe that the mysterious Indian man was the "telemarketer" from earlier.

Castle doesn’t have time to think about the new development, because Alexis calls him and asks him to come back to the office immediately … alone. Back at the office, Hayley is with Alexis. She doesn’t have much information, but she is willing to share what she knows -- if Castle keeps his police buddies out of it. The two explore a lead at a storage locker while Alexis investigates Beckett’s mystery man.

It turns out that Beckett’s “telemarketer” has diabetes. Alexis is able to find security footage that shows her stepmom breaking into an ambulance to steal some insulin before getting in a taxi. But why is she working with this man? And what are they doing? Castle and Hayley only add more questions to the mystery when they discover a storage locker full of guns … and a deadly female assassin. Fortunately, the two walk away unscratched, but the female assassin knows that they’re searching for Beckett.

Meanwhile, Alexis is able to track the taxi to an upstate prison -- the same prison where Beckett’s archnemesis, former Sen. William Bracken (Jack Coleman), is serving time. Why would Beckett visit the man who killed her mother? Castle speculates that Bracken wants payback after Beckett put him behind bars. Of course, Bracken doesn’t admit to anything when Castle visits him. But he does warn Castle that he doesn’t even “know” who his wife is.

Confused about his conversation with Bracken, Castle is distracted when he leaves the prison. The female assassin shows up and drugs him before tossing him into a truck. When Castle wakes up he meets a man who wants answers about Beckett … and is willing to do anything to get the information. But don’t worry, the man doesn’t plan on using his gun -- yet. Instead, he has a box full of tarantulas with which to torture Castle.

Castle doesn’t have any answers, and the assassins get frustrated. They place a plastic bag with the spiders in it over his head and are ready to shoot him when Castle manages to break out of his restraints. He knocks his captors over and makes a run for it, but is unable to escape the building. The female assassin is about to shoot him again when someone else fires a gun – Beckett.

Beckett explains that she couldn’t call him and that she can’t stay. But before she runs again she tells him that she loves him and gives him a quick kiss.

Fortunately, Alexis catches on quickly that her father was taken thanks to a tracking device she put on his phone. His phone is off, but Hayley has some information that the police use to track him to a warehouse. They detain the female assassin, but Beckett is gone by the time they arrive.

Back at the precinct, Esposito and Ryan are able to ID Beckett’s mystery accomplice as Vikram Singh, a low-level analyst for the U.S. attorney general’s office in Washington. It’s the same office that Beckett worked at two years prior, however Vikram is a new employee. The twist is that Beckett’s former partner, Rachel McCord, died in a car accident the previous day with three other members of her team. If that wasn’t suspicious enough, the fourth and final person of McCord’s team was stabbed to death at a nightclub the night before. That’s right, the female assassin was the woman from earlier in the episode who stabbed the man.

Why is the female assassin murdering people from the attorney general’s office? And why does she want Beckett dead? She’s not willing to talk, and warns Castle that while some of her associates are dead, there are more people ready to carry out the mission. While being transported she manages to break free and grab a gun from a police officer. She opens fire in the precinct, forcing Esposito and Ryan to shoot her dead. As Castle tells Alexis, she wasn’t trying to escape … she knew that her “fate was sealed.”

The “Castle” Season 8 premiere ends with Beckett at an apartment as a team of assassins -- led by the man who almost killed Castle -- arrive.