Horatio battles the FBI and U.S. Marshals as he tries to uncover why a woman was murdered at the side of a pool at a hotel. The investigation begins shortly after the woman is found dead from two shots to the head. The evidence suggests that it was a professional hit man, which is strange enough, but the case becomes additionally puzzling when the Feds and U.S. Marshals get involved. Plus, the murder weapon is linked to a cold case that was orinially investigated by Yelina. Meanwhile, Calleigh talks to her dad about his drinking problem after she's called away from work to drag him out of a bar.

The two young owners of a city bar are gunned down after hours and another man is wounded in the attack, which was allegedly committed by a masked gunman. Meanwhile, Calleigh's dad announces he is now a public defender and needs her help with a murder case in which a woman allegedly stabbed her boyfriend to death in his car with a screwdriver.

The CSIs must find the killer after a young woman is pushed in front of a moving bus. Alexx finds a bruise shaped like a hand imprint on the victim's back, proving that she was pushed in front of the bus, and her boyfriend, Jay Seaver, is the prime suspect. When one of Jay's office rivals also turns up dead, Jay reveals that he has a psychotic stalker, Claudia, who he thinks might kill to please him. However, when Jay hires a lawyer to protect Claudia, Horatio suspects that Jay may be more involved than they thought. Later, a man's body is discovered down an elevator shaft in a nearby building, and there is evidence to link the victims to a common killer. Meanwhile, Calleigh's father seeks her help when he fears that he may have killed someone after a night of drinking, and Horatio assigns a new CSI, Ryan Wolfe, to the case.

After a bitter custody battle, shots are fired outside the courthouse. Bullets fly and the target is the little girl's mother. Horatio goes after the father, who he suspects may not be the girl's biological father after all. However, when the mother's shady past is uncovered, the team finds that she has a lot of enemies who would like to take a shot at her. Meanwhile, Calleigh's father returns to the crime lab for her guidance but for an unexpected reason.