Season 1: Episode 19 - Allegiances

Allegiances : Carrie's relationship with Steve is put to the test when one of his best friends becomes the prime suspect in a double homicide.
One of Steve's restaurant suppliers, Michael Dal Bello, disappears after his girlfriend is found murdered in her apartment, and the team initially thinks he's the prime suspect. However, when Michael's body is discovered in a storage locker in an apparent mob hit, all the evidence begins to point toward Tommy Rugolo, one of Steve's best friends. Steve claims that Tommy is innocent, but Carrie doesn't fully believe him, creating a rift between them.
Carrie breaks protocol to warn Steve that Tommy is going to be arrested on suspicion of murder, and Steve meets with Tommy to try and get to the truth. The cops move in to arrest Tommy, who is gunned down when he fearfully pulls a weapon on the pursuing cops. Feeling guilty for the death of Steve's friend, Carrie goes to Webster to confirm that Tommy was actually the killer they were after, but Webster doesn't believe they got the right guy. She finds an adhesive residue on the body of one of the original victims that eventually leads Carrie and the team to the real murderer; one of mob don Joey Marzulla's men.
Carrie shares this information with Steve and apologizes, but it's not clear if their relationship can survive this...