Danny has to skip McGarrett's poker game to be a last-minute chaperone at Grace's formal. Grace is afraid that Danny is going to spy on her friends. Danny browbeats Will Grover to find out who Grace's boyfriend is, and Will admits it's him. Danny calls Grover to tell him about their children. Grace storms off, but Danny hauls away Will to talk with him. Cell-phone service cuts out at the dance. Then Danny and WIll hear gunfire, as five gunmen taken over the ballroom. The gunmen are looking for somone at the formal. Danny and Will crawl through the vents to get the school sign's control room, but Danny's claustrophobia slows him. They change the sign, but the lookout outside sees the sign and calls for another half-dozen gunmen. At the poker game, Grover is concerned that Will won't answer his texts and heads for the dance. Danny takes out first one, then two other gunmen, then gets pinned down by a fourth gunmen, who Will takes out with a fire extinguisher. Will figures out who the target is --- Jeremy Ramos, a diplomat's son. Grover gets turned around by the lookout. He spins around at the sound of gunfire, then wings the lookout. Soon the school is surrounded by cops. Grover interrogates the lookout, and they figure out that the terrorists want Jeremy to trade him for an imam about to be executed. They threaten Grace and Danny and Jeremy come out of hiding. The terrorists give McGarrett an hour to arrange the trade, but that can't be done, since the imam is already dead. Grover calls Will, who is hiding, and has him scout the situation. The cops storm the ballroom and take out the terrorists. Will and Grace dance at a diner afterward, while Grover and Danny talk about their changed situation outside.