Modern-day NYPD Detective Sam Tyler finds himself suddenly hurtled back to the tumultuous times of New York City in 1973 when he's hit by a car while chasing down a criminal.

Is this vintage 1973 Sam Tyler real or not? Sam's unbelieving ears clearly hear a radio station announcing that Elvis will perform a concert in memory of his mother, but he's still not sure how or why he landed in these circumstances. Moreover, he doesn't have much time to think about his own predicament. A string of fatal robberies at AAA Money check cashing stores are baffling the 1-2-5, and Sam jumps headlong into the case, which features no forced entries and no witnesses. Even with Lt. Hunt strong-arming the lead suspect, it still takes an unexpected turn of events to make the squad to look within to solve the crime. At the end of the day Sam, in spite of himself, might even experience some true happiness - temporary though it might be.

The murder of a returning Vietnam veteran has Lieutenant Hunt outraged, as he demands a quick resolution to what quickly becomes a complicated and controversial case. As Sam and the squad's team of detectives explore the circumstances surrounding the homicide, Tyler is sent down a mysterious path that may provide clues about his own family's past and why he is back in 1973

Sam is unwillingly but hypnotically pulled back into his childhood when he becomes entangled in local gangster Nick Profaci's assault on a young, beautiful woman. Sam is amazed to discover that the woman, who is oddly familiar to him, is actually his mother back in 1973. While he anxiously attempts to save her, he uncovers two unsolved murders of women that possibly point to the involvement of Profaci and his mob boss, Elliot Casso's. But even more alarming is the discovery that members of the 1-2-5 - including Lt. Hunt - may be mixed up with Casso and his crew and may have prevented justice from being carried out.

A racial confrontation is triggered between the African Americans and Puerto Ricans in the neighborhood when a young African American girl's body is discovered thrown from a rooftop. Working the case with Sam Tyler and the squad is the cop Sam considers his mentor in 2008 - a much younger Fletcher Bellow - who doesn't recognize his future protege. Tangling with the Black Liberation Army, who is intent on hunting down the Puerto Rican suspect first to levy their own kind of justice, Sam, Bellow and the detectives of the 1-2-5 are in a race against time if Angel Ramirez is to have any chance to answer for the crime. But in the end, Sam must battle the racial attitudes in his own precinct - most notably Lt. Hunt and Detective Carling - and a dramatic standoff on the same rooftop leads to gunshots being fired.

With a life-and-death hostage situation paralleling own strange circumstances, Sam Tyler is ordered with the rest of the 1-2-5 to diffuse a potentially deadly face-off at a hospital where a crazed gunman is trying to force a doctor to reverse a dangerous operation on the renegade's brother, and the squad are all targeted in the gunman's cross-hairs.

When the baby of a prominent family is kidnapped for ransom, Sam Tyler is shocked to discover that his own father, Vic Tyler, may be involved. Sam's discovery leads him to face some deep dark secrets about his childhood.

Lt. Hunt's squad and Lt. Nunzio's crew renew their long-standing rivalry due to a bank robbery with a connection to the Russian mob. Meanwhile, Sam is attracted to a pretty, young social worker.

Ray's shady brother may have played a role in the number of recent decapitations in which the squad is investigating. but other suspects pop up too, such as a biker, a Wall Street executive and badly disfigured man.

When rock star Sebastian Grace receives a death threat, Sam and Chris are exposed to the rock-and-roll lifestyle that includes one of Grace's groupies called "Rocket Girl." Things really get strange when Chris finds Sebastian and Rocket Girl waiting for UFOs in the swampy area of New Jersey known as the Meadowlands.

NYC Councilman Bobby Prince shares a secret with Sam after Prince is caught with a hooker during a raid on a motel. The secret leaves Sam with even more questions as well as the realization he has more in common with Prince than he had ever thought. Meanwhile, Gene Hunt locks down the precinct after a shooting, Maria and her father confront each other, and Ray's wife, Denise, adds tension to the drama.

The detectives at the 1-2-5 investigate the murder of newspaper journalist Joey Conway. Sam is convinced the killer is the same criminal from a case in 2008. He is motivated by flashbacks to the case, which puts him at odds with his coworkers who think someone else is guilty.

When the Weather Underground sends the department bomb threats on the anniversary of their leader's death, Lt. Hunt takes the threats personally. As Sam, Annie and Lt. Hunt investigate, they soon find a connection between a student and Pat Olsen, a professor.

When a Pan Atlantic air hostess is found dead, Annie volunteers to go undercover in order to solve a series of homicides. Annie, Sam and Ray, working undercover, are able to find an unlikely suspect.

When Sam goes undercover as a gang member, he has to reveal a dark side in order to keep his cover. While undercover, Sam is pushed to the limit when he is ordered to bind and shoot a woman.

Crime hits home after Ray and Chris are shot by a gang member. When the shooter is found dead near a bar, Sam becomes the lead suspect since he has been working undercover as part of the gang. With evidence mounting against him, Sam must search for the real killer before it's too late for him

When Sam Tyler receives a phone call that presents him with three tasks he must perform so he can return to his life in the future, he must weigh his alternatives and decide whether to stay in 1973 or go home.