A murdered real estate agent is found in the walls of one of his listings and Five-0 discovers the murder weapon was used in another crime, confiscated, and should have been destroyed. Chin and Kono take down the illegal gun selling operation that leads them to the killer - a lawyer whose wife was having an affair with the agent.
Meanwhile, McGarrett helps protect Grover from a prying reporter inquiring about Chicago and Grover must come clean to McGarrett. Danny's mom arrives in Hawaii and she reveals she's divorcing Danny's father before she admits to feeling lonely.