Beckett hasn't heard from Castle since he left for the Hamptons months ago to finish writing his second Nikki Heat novel, "Naked Heat." The most Beckett, Ryan and Esposito have seen of Castle is a bookstore standee of him advertising an upcoming book signing. So when Beckett and her team burst into a shadowy apartment on the trail of a murderer, the last thing they expect to see is the real-life Castle standing over a dead woman's body holding a gun. As Castle protests his innocence, Beckett has no choice but to arrest him on suspicion of murder.

When a famous psychic is murdered, Beckett and Castle search for her killer while also carrying on a spirited debate on the existence of extrasensory abilities. Evidence mounts on both sides, especially when a letter arrives from the victim, penned the day she was killed and predicting her own death -- or was it written by a clever killer, hoping to throw off the investigation?

When a coded document hidden by a murdered bail bondsman gets Castle's imagination running wild, Beckett must steer the case back to the violent felons who populated their victim's world - only to discover that maybe Castle's crazy theories aren't so crazy after all. Complicating matters is the surprise arrival of Beckett's ex-partner (now a bounty hunter). As the two reunite over a history that Castle has no part of, Castle is forced to watch the relationship take a turn towards the romantic.

When a mathematician is killed by a 200-year-old bullet, Castle comes up with time-traveling theories.

Mysteries abound when pallbearers at a funeral lose control of a surprisingly heavy casket only to have a second unknown woman tumble out along with the original deceased. When Castle and Beckett learn that the victim was a doctor at County Hospital, their investigation takes them into the world of amorous, bed-hopping physicians. Did jealousy turn to murder, or did the doctor's mysterious work outside the hospital lead to her demise? Meanwhile, Castle's relationship with Gina is challenged when she tries to bond with Alexis.

When a beautiful woman is found dead in an alley, all clues point to her being a victim of the notorious Triple Killer. The Triple Killer, or 3XK, terrorized New York City four years ago, then mysteriously disappeared. Now he's back. In a deadly battle of wits, Castle and Beckett race against time to stop 3XK before he claims his next victims.

Responding to an "Officer Down" emergency call, Castle and Beckett's latest case takes a shocking turn when it's revealed that the victim isn't a cop but a male stripper dressed up as one. The murder leads them into the world of male strip clubs, the hardships of struggling actors, and the price that people pay in pursuit of fame. Did our victim's dreams of stardom get him killed, or was there something more nefarious afoot?

A subway worker is found dead after witnessing the kidnapping of a twelve-year-old boy.

Astrophysicist Marie Subbarao (35)'s corpse is found, with all symptoms of fatal explosive decompression. Her ex Ted Carter, a colleague at the institute, has an alibi. An SF author friend also points to Castle's remark that everything seems to point to aliens. However the team's digging leads to FBI agent Westfield, whose agency goes to extraordinary lengths to stop their investigation, yet fails to keep from them Chinese Ung Kyu's involvement.

The death of a bar owner takes Castle and Beckett back in time to the prohibition era.

An actress playing Nikki Heat shadows Castle and Beckett on the death of a matchmaker. Meanwhile, Ryan plans on proposing to Jenny.

When the owner of historic Drake's Magic Shop in New York is found drowned in Houdini's famous water torture tank, Castle and Beckett must delve into the world of magic, magicians and their secrets to find his killer. As part of their investigation, Castle & Beckett meet master magician Tobias Strange. Meanwhile, the magicians aren't the only ones keeping secrets, as a new romantic relationship is revealed for Esposito and Lanie.

The detective on Beckett's mother's homicide case is killed after telling her he has information.

Lottery-multimillionaire Jay Hixton is shot in the heart at home around midnight. He was apparently forced to open his safe. It contained a gun even butler Reginald Easley didn't know about, which was laid besides him, and a bag, which was taken, containing $100,000 cash and a blue dye bomb, which exploded in a maintenance worker's face. Various suspects arise from Hixton's bizarre generosity, his own murky past and his family, an ex and junkie daughter, and even his winning lottery ticket a year ago.

Castle fights to help an old boarding school friend when be is accused of killing his wife.

Recent US citizen Amir Alhabi, an immigrant from Syria, is found dead in a building next to where his stripped cab is found. He and his cousin Jamal were the owners of the cab. Investigation of the cab's GPS shows that Amir picked up a fare earlier in the day, drove in a circle and then let him out at the same spot. The fare is identified as Fariq Yusef, a 'security attache' for the Syrian Embassy. When Castle and Beckett go to investigate a storage locker, identified from a note on Amir's phone, they find a weapons cache and are exposed to radioactive Cobalt 60. Homeland Security Agent Mark Fallon takes charge as Amir used to work in the Syrian weapons program and it is feared he created a nuclear weapon. Suspecting something didn't feel right, Castle, with Beckett's help, contacts Fariq Yusef to get more information. When Agent Fallon finds out, they are both removed from the precinct. Unofficially, they keep looking into tracing a payment to Amir and why he had a camera installed in his cab. This leads to a fake cover-up, shifting focus to cab driver Kevin McCann.

With time running out, Castle and Beckett must put aside their differences with Agent Fallon to avert a city-wide catastrophe.

A writer of a popular soap opera is found dead. Castle and Beckett come across cheating husbands, mistresses, backstabbers and a con artist to find the killer.

Juror #7 Joe McUsic, who runs a halfway house, drops dead of cyanide-poisoning during Otis Williams's high-profile trial for the murder of heiress Lyla Addison. Juror #4 Tony Mueller runs as he believed Otis's cousin, Wardell, poisoned Joe and he'd be next. Wardell claims he is being framed just as the cops are trying to frame Otis. The cyanide came not from the court house vending machine coffee but was released from a capsule. The plot thickens when it was found that Joe McUsic used a bribe to be put into the jury pool. The case is complicated as there doesn't appear to be any link between Joe McUsic, Otis Williams or Lyla Addison.

Castle knows of four pizzerias named "Nick," with various combinations of the predicates terrific and/or authentic. But their owners, bitter rivals, continually sabotage each other with frat pranks. Then a corpse is found in the pizzeria oven, crisped, but killed by previous stabbing. The owner accuses his rivals, but no one is innocent and everyone has a dirty secret. And the victim, a former war correspondent who lost his edge after his daughter died in a car accident, was reporting on them about their "pizza wars." However, he'd also stumbled across the identity of 'urban myth' Cavallo, a drug lord who viciously executes rivals.

When a champion swimmer and Olympic hopeful is found dead in a training pool, Castle and Beckett dive in to investigate his murder, and uncover myriad secrets that might have led to his death.

When Beckett's old training officer is killed, she takes off on a solo mission to find the killer. On the plane she runs into Castle who is flying out to the Heat Wave movie set. She lets him help her catch the killer.

Mysterious murder occurs during a beauty pageant and the suspects are plentiful.

Cop killer Hal Lockwood, whom Beckett visited unsuccessfully in jail for months hoping for a lead in her mother Johanna's closed murder case, is released by a faked order into the general population, where he slices rogue cop Gary McCallister's throat, then is helped by fake cops to escape. Beckett, his likely next target, receives warnings from her father, Montgomery and Castle. Much helped by Ryan and Esposito, the duo work out that there must be a police accomplice and/or mastermind controlling Chuck Ryker, the debt-ridden corrupt jailer who was found murdered at his home.