After what felt like an eternally long hiatus, Castle is back in full swing. And what better way to celebrate than a little fun in the sun with our favorite detectives.

Mike Royce has been murdered. Shot dead in cold blood. You all remember Royce, right? Beckett’s old training officer? If not, do yourself a favor and stop reading this now, then go watch “Under the Gun” (3×4). You can thank me later. The interesting part about this case is, in not so typical Castle fashion, we see who the murderer is right at the beginning of the episode. Special guest star Dominic Purcell is to blame for killing Beckett’s former mentor. But just before Royce bites the big one, he assures Dominic Purcell’s character that hell is going to reign down on him for killing him. The assassin seems unfazed.

Beckett has a hard time dealing with Royce’s death, and rightfully so. This was, after all, a man she was once in love with. The only two pieces of evidence found on Royce’s body are a plane ticket that tells them he only just got to town, from L.A., and a letter addressed to Beckett. Ryan and Esposito find the murder weapon a few blocks away, a gun with a silencer missing, which is enough to start them looking in the right direction.

Armed with the new information, the team uses it to narrow their field of suspects to people who flew from L.A. to New York and back again in a matter of hours. They focus on the flights that followed Royce’s, and people who purchased tickets at the last minute. Luckily, only one name popped, a Neel McCauley. The man bought his ticket at the airport an hour before the flight and from what Ryan can ascertain, all his background information is fake. Then it dawns on Castle, Neel McCauley is Robert De Niro’s character in the movie “Heat.” Unfortunately, the man also left town two hours after Royce was shot.

Beckett requests to go to L.A., fighting Captain Montgomery tooth and nail about it, but he won’t let her go. She’s too close to the case, the last thing Montgomery wants is for Beckett to get in over her head and do something stupid. After being denied, Beckett opts to use some vacation days she has coming. She lies, point blank, to the Captain’s face about dropping the case. Castle doesn’t buy her act about going home either, but Beckett insists she’s just going home because she needs some time alone to deal with the death of her friend.

After reading Royce’s letter to her, Beckett hops a plane to L.A., against orders, of course. And as with most of us unfortunate enough to travel in Coach, Beckett finds herself sandwiched in between two rather large men. This is why no one ever requests a middle seat. As if that weren’t bad enough, somewhere from the back of the plane, a baby begins to cry. But then a merciful flight attendant comes along and requests Beckett by name. Beckett doesn’t even question it when the woman upgrades her to First Class. She just happily rolls with the punches. Seems too good to be true, right? Well, it is. When Beckett arrives at the seat number given to her by the flight attendant, she finds Castle already sitting in the window seat, glass of champagne in hand. Beckett doesn’t want Castle along for the ride because she’s not a cop in L.A. She has no jurisdiction and is therefore going rogue. Castle assures her that he’s only there to visit the set of his new movie, “Heat Wave,” but going rogue does happen to be a specialty of his.

Once in L.A., Castle realizes Beckett’s hotel is all the way in the Valley. The Valley, people. This just won’t do. So, he offers to let her stay at his hotel with him, since the studio conveniently comped him a two bedroom suite. Don’t we all wish we were so lucky.

The first stop on the Homes of Hollywood Stars tour, er, I mean, the address on Royce’s driver’s license, leads them to the home of Gene Simmons. That’s right, THE Gene Simmons. A little conversation with Gene reveals that Royce was in the business of helping people out of trouble, and since he’d helped Gene out of a bind recently, Gene let him stay in his guest house in return. Gene remembers Royce was helping someone else, he doesn’t remember the woman’s name, but since it’s Hollywood, she of course left a headshot behind. The woman’s name is Violet Young, a wannabe starlet with only one movie credited to her name.

Meanwhile, back in New York, Ryan and Esposito are still working the case on their end. They get lucky and find some video surveillance footage of the assassin. It’s too blurry to make out his face, but if they can ID him by his clothing in airport surveillance footage, they just may have their man.

Back in L.A., Castle and Beckett head to Zenith Studios (This is actually the studio where Castle is filmed. Meta, anyone?) where Violet was supposed to be filming a commercial. Zenith Studios also happens to be where they’re shooting “Heat Wave,” so Castle can pay a little visit to the set while he’s there. Beckett goes off to find out if Violet showed up for the commercial, while Castle meets with the actors playing Rayley and Ochoa in the film. Beckett returns to tell Castle that Violet missed work, something she wouldn’t have done since it was such a big break for her. She also gets to meet the big screen versions of Ryan and Esposito but finds them a little too creepy for her taste.

Once again in New York, Esposito goes to visit his favorite ME, and girlfriend, Lanie for some information on the bullets used to kill Royce. He wants to take them over to ballistics, but unfortunately they’ve both dissolved into puddles of foamy goop.

Beckett uses her excellent lock picking skills in L.A. to break into Violet’s home when she doesn’t answer her door. A search of Violet’s home reveals it’s empty, but they do find a notepad with flight information on it, the same flight Royce took to New York. Violet had gone with him. They also discover a pile of photographs taken of an unidentified man. Just when they have a promising lead, the LAPD shows up to arrest the pair for breaking and entering. Detective Kyle Seeger (guest star D.B. Sweeney) is called in to deal with the duo. Seeger calls Captain Montgomery, who promptly chews Beckett out and insists she and Castle get on the next flight home. But Beckett didn’t listen the last time he told her not to do something and she’s not going to start now.

Beckett enlists the aid of Ryan and Esposito to find Violet while she and Castle go to find their mystery man. Castle discovers the man is Charles Kelvin (guest star Jason George), CEO of Kelvin North America. His company was making the top secret dissolving bullets in order to win a defense contract, the same bullets he soon realizes are missing from the company vault thanks to Violet.

Ryan traces Violet back to an ex-boyfriend’s apartment, but she only stayed one night and stole the man’s wallet in the morning. A man showed up looking for Violet not long after, giving the ex a good beating for his trouble. Now armed with a sketch of their suspect, Ryan hopes they can find Violet before he does.

Settled in at the hotel, Castle and Beckett run theories with the information they have so far. Beckett begins to reminisce about Royce, sharing a few stories with Castle. She’s still in shock that he’s dead. Castle decides to take her mind off of things by telling her why she’s so special. They share a moment before Beckett panics and says goodnight, heading straight to her bedroom. Castle stares at her closed door a few seconds longer, hoping she’ll return, but when she doesn’t he retreats to his own room for the night. Beckett struggles with her decision for several moments before she reopens her door, only to discover Castle is already gone.

The next morning, thanks to the ever so helpful hotel concierge, Beckett sets up a murder board in their hotel room. She fills Castle in on what they know so far, but a knock on their door has her hiding the board in her bedroom. It’s a good thing too since Detective Seeger pays them a surprise visit. Castle thinks they should play nice with the detective, especially since they may need him in the future, but Beckett has a better idea.

With the help of fake Ryan and Esposito, Beckett pretends to be an LAPD detective to pick up Reggie Walsh, a security guard on duty the night of the theft at Kelvin North America. Castle and Beckett interrogate the man on an interrogation room set at Zenith Studios, the guard confessing to taking a bribe in order to take a cigarette break at the time of the theft. He identifies the sketch of the man hunting Violet, as well as an image from airport security of the assassin who killed Royce, a man he heard referred to as Ganz. A quick call to Ryan turns up a connection between Ganz and an associate of his named Mannis. Mannis’ mug shot matches the sketch of the man who’s been hunting Violet.

Castle calls upon the all too friendly hotel concierge for help, figuring since Ganz is a man of wealth, he may be well known in certain circles. He would be right. The concierge does know of Ganz, specifically that he likes to conduct all his business poolside. According to the concierge, Ganz likes to be surrounded by beautiful woman as he works by the pool, which he is currently doing as they speak. Castle thinks it’s time to call in the LAPD, but Beckett has a better idea.

In a very Sydney Bristow-esque moment, Beckett emerges from the pool, dripping wet and looking very sexy in her swimsuit, right in the line of Ganz’s sight. He instantly takes notice in her, and who wouldn’t, leaving his cabana, and his phone, unattended while he goes to talk to her. Beckett uses a magical accent while introducing herself as Lola Black, and I say magical because it disappears and reappears several times throughout the conversation. While Beckett is busy working her charm on Ganz, Castle sneaks into the man’s cabana and photographs the recent call list on his phone. Beckett tries a little too hard to keep Ganz distracted and he makes her for a cop, which doesn’t sit well with Beckett. Poor Castle is on the receiving end of her wrath for blowing her cover, but Beckett’s rage quickly dissipates when she learns what Castle did. Castle thinks it’s now time to call in the LAPD, and Beckett finally agrees.

Now that Castle and Beckett are working with Detective Seeger, they’re willing to share information. Seeger briefs them about the connection he found between Ganz and Mannis, a phone number, and the trio decides to call it in hopes of setting their suspects up.

Back in New York, Ryan and Esposito have found Violet. Too bad Mannis has too. Just as Mannis is about to get the drop on Ryan and Esposito, his phone rings and tips them off. Esposito shoots Mannis and answers the man’s ringing phone, surprised to hear Beckett’s voice on the other end. Esposito gets Mannis to turn on Ganz, confessing Ganz was the one who shot Royce, and that his deal to sell the stolen bullets is taking place on the Santa Monica Pier at six o’clock.

Beckett, Castle and Seeger head down to the pier to catch Ganz in the act. They find the van and apprehend the driver, but Ganz is nowhere to be seen. While Castle is busy with Seeger, Beckett goes in search of Ganz. She spots him walking off the pier and quickly follows him, but Ganz makes her and sprints down the pier. He jumps off the pier into the sand, running underneath the pier to get away, but Beckett stays on him, jumping off the dock herself and following him beneath the pier. She finds herself alone with Ganz, loaded weapon in hand, and gets really close to pulling the trigger. But just as she’s struggling with the decision, Castle and the LAPD catch up with her, and Seeger and company take Ganz into custody.

With the case solved and Royce’s killer now behind bars, Castle and Beckett head home. While on the plane, Beckett rereads Royce’s letter. In the letter Royce tells her he knows she has something special with Castle, and to seize the moment before it’s too late. She doesn’t want to spend her life thinking, “if only.” Beckett smiles to herself and glances over at Castle, who is fast asleep in the seat beside her.

Things We Learned From This Episode:

* Castle has gotten extremely comfortable with calling Beckett by her first name, especially in this episode.

* Castle dates Parisian supermodels.

* Castle and Beckett have both dressed up as Gene Simmons for Halloween. If that’s not kismet, I don’t know what is.

* Relationships are made and broken based on timing, and Castle and Beckett really need to work on theirs.

* Beckett is finally willing to admit she finds Castle attractive, even if it with a great deal of subtlety, while Castle opening gawks at her.

* Ryan and Esposito are terrible liars.

Written by Stephanie Guenzler. Find her on Twitter @pure_believer