The Guardian is about a Coast Guard rescue swimmer named Ben Randall. Ben has been at the top of his field for some time as part of the Aviation Survival Technician program. Ben is having issues at home and his wife decides to ask him for a divorce. On this same day, Ben is called to a dangerous rescue at sea. His helicopter crashes and Ben loses his crew and his best friend. All of these circumstances shatter Ben emotionally and he decides that he must either retire from service or teach in the AST program. He opts to instruct young recruits.
Meanwhile, Jake Fischer has decided to forgo a swimming scholarship at a prestigious university to enlist in the Coast Guard. Jake's goal is to be the best swimmer in the AST program and to become a bigger legend than Ben.
When Jake first enters the training academy, he meets Emily Thomas. Emily is a local school teacher. The two hit it off instantly and Jake winds up sleeping at Emily's house. He is then late for class the next day, which raises the ire of Ben. This begins the clash of egos between the two. However, Ben realizes the dedication Jake has for the program, and stops making life so difficult for Jake.
The two find common ground through more revelations and start to form a strong friendship. Jake eventually graduates from the AST program and assumes Ben's old post.
The two men eventually have to go on a dangerous rescue together as a capsized ship in the Pacific requires the two best swimmers the station has. Ben has to save Jake during the dangerous rescue, and Jake tries to return the favor. However, one of the friends must make a major sacrifice to ensure the safety of the other.