The episode opens at an FBI safe house out in the middle of nowhere. A marshal is protecting a witness in a trial when their police escort shows up to take them to court. Unfortunately, the real escort has been killed and these are assassins targeting the witness.
There are really two stories to this episode. The first is related to the witness, as McGarrett and Chin look for both her and the assassins. The second is related to Danny’s ex-wife. She and their daughter are carjacked whilst in her husband’s car. They are okay, and the car later turns up. Then their house is broken into. Danny believes that it wasn’t an actual carjacking, but something related to her husband, who is presumably in trouble.
This episode’s name means “Protect and Serve”.