Alejandro Vega, known as El Diablo, a wounded serial killer, is arrested by the FBI outside a bakery. A hurricane is bearing down on Oahu. Rachel and Charlie arrive to stay with Danny during the storm. McGarrett sends out Tani and Junior on safety checks. The FBI gets permission to stash Vega at Five-0 headquarters during the storm. An assassin is tracking Vega and has blended in with the civilians being evacuated to the Palace. A couple with a little girl refuses to evacuate, and the man pulls a gun on Tani. The power goes out, then the backup generator comes on, but Vega is still locked up. Somebody sliced wires to the in-house cameras, and a deputy has been stabbed. Grover and Jerry work to stabilize the deputy, Haku. Jerry had seen the attacker Haku described earlier. Junior can't reach Tani, who is tied up. Tani convinces the daughter Emmy to untie her. Jerry identifies the assassin from his tattoo, and he's from a rival gang, there to kill Vega, who has turned state's evidence against his enemies. The killer is pumping exhaust into Vega's cell. McGarrett and FBI Agent Collins rescue and resuscitate Vega and moves him to Steve's office. Tani gets the gun away from Jameson, but finds out she's at a stash house, with more thugs showing up. The assassin kills several FBI agents, then battles with McGarrett, with Steve coming out on top. Vega escapes from the elevator during the fight. Tani takes out two thugs, then Junior kills the third. Vega tries to hotwire a car, but the FBI mole Harris comes after him. McGarrett shoots Harris before that he can kill Vega. Rachel and Danny fell asleep together on the couch. McGarrett stops by to grill Danny about his night.