Spartan begins in a training camp. Scott is overlooking the training of Curtis. He endures some tests and is recruited into Scott's team. The situation arises that Laura Newton, the daughter of high ranking U.S. government official, is missing. There are three days left before the press will say she hasn't appeared at her next class.
Scott begins investigating by interrogating the secret service guard supposed to be on duty at the time of her abduction. He denies not being at his post. Scott then tails the boyfriend of Laura while posing as a security guard. He catches him in the act of breaking into her mailbox. The boyfriend is trying to get rid of incriminating evidence of threatening her so he tells Scott of a bar where prostitution happens. The evidence is a note where she signs it with a particular symbol. %-)
Scott and Curtis
Back at H.Q. the guard commits suicide shortly after Curtis appears. Scott and Curtis go to the bar, Black Light, and Scott disguises himself as a wealthy man looking for some fun. He meets up with the pimp that discloses of Boston bordello after some coercion. At the bordello he convinces the prostitute to tell him what she knows. Shortly after he roughs up the bordello's mistress to the next lead.
The lead goes to a beach house that looks empty except for a few lights on. Curtis covers Scott as he infiltrates the house. He makes it in and kills one thug while Curtis shoots the other. As he is sniping, Curtis notices the symbol on the window. Laura is still missing and no further leads are in the house.
Next option becomes a man in prison being transported the next day. Tariq Asani has called the bordello recently a few times and is connected. Scott sets up an elaborate ruse as no nonsense robber. Tariq and a convict on death row are in the back seat of a police vehicle while Scott shoots up the rural gas station. He guns the police officer and lets the convicts out of the car. Scott goes back inside and continues the farce of robbing the place. Outside he shoots the convict and Tariq pleads that he can get a plane for both of them. Tariq spills some information of a prostitution operation in Dubai and a place they use to clean up the girls before transportation. His neck bleeds so they take a stop at a rural convenience store. Scott goes inside and grabs Curtis's gun and ammo. Curtis does the same with another agent but in view of Tariq. He shoots Curtis with a shotgun and Scott guns him down.
An operation is being set up to invade the Dubai bordello when the news speaks of Laura and her professor are dead. They say the bodies are washed up ashore from a boating accident in Martha's Vineyard. With the case closed Scott goes on leave in some rural place. Curtis tracks him down and convinces Scott that Laura is still alive. He found her earring later from the beach house. So they go back and retrace the evidence. While a boat along the coast has a sniper and takes out Curtis. Scott escapes and finds a tracking bug in his phone.
He goes to Laura's mother surrounded by secret service agents and meets Laura's caretaker. Afterwords he meets up with Jackie Black for advice and then sets up the operation with an information broker. On the flight to Dubai, he examines photos of the bordello and sees Laura's symbol in the window. In Dubai, he starts the preparation of Laura's rescue with a mercenary. During the initial overlook of the bordello they see Laura being transported. They shoot their way through the guards. The mercenary is killed while Scott runs off with Laura to his safe house.
They move along their primary plan of using a cargo container to transport Laura. Scott makes a cigarette for Laura and cleans out his knife. Inside the handle is another tracking bug. They escape inside of a hangar where Scott gets shot by one of Stoddard's men. Jackie Black escorts Laura to a nearby airplane with Swedish journalists. Stoddard shoots Jackie, Laura makes it safely inside the plane, and Scott slits Stoddard's throat. As the plane lifts off, Scott holds Jackie until she dies.
The movie ends with a news report of Laura's return on TV, with Burch seemingly taking credit for the operation. Scott is revealed to be watching the TV, now with a beard. He then walks away through a crowded London plaza.