discover a serial killer who has been operating for at least thirty years with an unknown number of victims, all people who won't be missed. The investigation leads them to the identity of the girl Castle saw murdered and a showdown between Castle and the killer after he breaks into the man's barn in search of evidence. Castle is forced to fatally shoot the killer in self-defense with Beckett's gun and brings closure to his victims though the incident leaves him shaken. Private investigator After being banned from the 12th Precinct, Castle completed online courses and became a fully licensed private investigator, hoping that he could still work with the department by conducting his own investigations rather than as part of theirs, but was informed that this planned loophole wouldn't work as he still wasn't allowed to directly come in contact with evidence. He continued to operate as a P.I., but soon found himself dissatisfied with the role, as he was mainly hired for minor cases or people viewing his new career as a 'gimmick' rather than a serious profession; one case saw him hired by someone who wanted him to act as a fake witness to her plans to fake her own death. However, after rescuing Beckett from his old nemesis the Triple Killer, Captain Gates eventually re-hired Castle as a consultant for the 12th precinct-'officially' designating it as community service for interfering in an active case-also reinstating him as Beckett's partner. After Gates and Beckett are promoted so that Beckett is now captain of the 12th precinct, Castle re-opens Richard Castle Investigations (his private investigator's office) to allow him to take part in investigations due to Beckett's more deskbound role. Literature As a promotion for the show, "Richard Castle's" book Heat Wave was released in hardcover by Hyperion on September 29, 2009 and debuted at No. 26 on The New York Times Best Seller list. In its fourth week on the list, Heat Wave broke into the top 10 as No. 6. Heat Wave was released in paperback on July 27, 2010 and debuted at No. 34 on The New York Times best seller Paperback Mass-Market list. The novel features a fictionalized version of the already fictional Richard Castle, named "Jameson Rook", who enters into a partnership with Heat that mirrors Castle's working relationship with Beckett. The second novel, Naked Heat, was released September 28, 2010, and debuted