Horatio Caine worked in New York City as a detective with theNYPD Before he moved to Miami at first as a detective then a Lieutenant with the MDPD. It was there that he killed the man who murdered his mother: his own father. In 1995, while on the job, he was stabbed while investigating a case in which children were locked in closets while their parents were murdered. The perpetrator, Walter Resden, harbored a deep grudge against Caine, collecting the blood from the stabbing and preserving it for 10 years in order to frame him for the murder of Caine's girlfriend, Rachel Turner.
After his arrival in Florida, Horatio joined the Miami-Dade Police as a homicide detective but later transferred to the bomb squad, where he was mentored by Al Humphries, an older cop whom Caine highly respected and considered a good friend; Humphries was later killed after accidentally triggering a bomb he was attempting to disarm. Horatio worked undercover as "John Walden" in Pensacola, Florida for sometime during the early 1990s (this is the date given on the show, despite the fact it was previously understood on the show that Horatio worked in New York until at least 1995). During his time there, he dated a woman he believed to be named Julia Eberlie, and the two conceived a son named Kyle. Horatio would not be aware of Kyle's existence for another sixteen years. Sometime later he returns to Miami and to being a detective, in "Out Of Time" he references previously working on the bomb squad. Finally, Caine moved to the Crime Lab, accepting a promotion to lieutenant, which earned him the animosity of Sergeant Rick Stetler, who was also vying for the position. When veteran CSI Megan Donner went on personal leave following the death of her husband, Horatio became the permanent head of the lab. Caine is known for regularly wearing sunglasses; one of his trademarks is to put them on prior to making a dramatized remark.
In the Season 9 finale, Horatio is shot down, and co-worker Natalia Boa Vista is kidnapped and put in the trunk of a car by Randy North, a man helped convicted felon Jack Toller after was threatened to lose his kids by Toller. While Randy is pointing a gun at Natalia's face, she is trying to talk him out of doing something bad. North said "That's what everybody has told me!", and then closes the trunk with Natalia inside and pushes it off the pier. After North pushes the car away, Horatio gains ability to attempt to shoot North, but was unsuccessful. Horatio is unable to stand and attempt stop the car with Natalia inside. Natalia uses her cell phone to call for help, but nobody answers as water drips over her.
In the 10th season premiere, Horatio begins to have hallucinations of Marisol, saying she is glad to see him but he needs to go back. He is next shown back at the dock where he was shot, managing to get himself back up to his feet. Still bleeding from his gunshot wound, he jumps into the water to save Natalia, managing to free her from the car. As they are rushed to the hospital, he repeatedly calls Marisol's name. Against doctor's advice, and still visibly in pain, he leaves the hospital to work on the case. He and the team manage to find North, and they try to get him to tell them where Toller is. Despite setting him up, Toller slips through his fingers once at a railyard, but Walter discovers that the chemicals in the soot from Tollers old clothes could only have come from trash burned at a particular landfill. Horatio manages to find and capture Toller there after he very nearly sets another woman on fire. After leading Toller back to jail, Horatio finally concedes that he is not all right and agrees to get checked out