McGarrett, the team and CIA Analyst Jenna Kaye stage an assault on a safe-house they believe is being used by Wo Fat, however, when they enter, they find themselves in pursuit of Sang Min. Sang Min escapes, but Danny finds a dead body in one of the houses they enter during the chase. Shortly after checking for a pulse, Danny starts convulsing and Jenny Kaye recognizes that he, and probably the victim have been exposed to a neurotoxin (turns out to be Sarin). While Danny recovers, McGarrett and the team work on the murder they stumbled upon. The victim was a homeless man who was given permission to squat in the house by its caretaker. The house is owned by a mainlander who owns a container manufacturing company who visits infrequently, however, he and his wife were supposed to visit the previous week and had cancelled their plans, making it clear, they were the intended victims. The owner's brother-in-law runs the operation in Hawaii and our team figures out that the brother-in-law has been using the house for romantic liaisons with his secretary. The team also runs a trace on the Sarin and discovers it's from a batch connected to a Russian group and the arms dealer is on the island. Turns out the arms dealer purchased containers to hold the Sarin, which leads us back to the brother-in-law. However, when they question him, they realize he didn't do it but his secretary did.
As Danny recovers, Rachel rushes to his side and tells him that she's leaving Stan.