In an episode that jumps backwards and forwards in time, Five-0 must track down and stop all the members of a terrorist cell looking to blow up multiple locations on Oahu. The episode begins with a flashback to Danny's days in New Jersey, as he tells McGarrett a story while they stake out the home of Hasan Fadhi, their suspect in an attempted bombing. The story is interrupted when Fadhi returns home and Five-0 gives chase. Danny shoots and kills Fadhi, but then discovers that he's wearing a suicide bomb vest rigged to explode at the slightest movement or touch. We then flash back to earlier in the day and learn how a would-be terrorist accidentally killed himself with his own bomb, and Five-0's involvement ended up preventing a second bombing during a memorial service at Pearl Harbor. Eventually, all roads lead to Fadhi as the bombing mastermind, and we resume present-time with clips of the stakeout, chase, and discovery of the suicide bomb vest. As the bomb squad tech works on disarming the vest, McGarrett gets Danny to continue his story about New Jersey, keeping his mind off the stressful situation. After a few heart-pounding seconds and a near detonation, the vest is finally disarmed and everyone is safe. Danny then races off to a father-daughter dance at Grace's school, keeping a promise he made to her earlier in the episode.
Danny's story about his time in New Jersey is told through flashback. It takes place 10 years ago, when he and his partner, Grace Cassidy, went to investigate a lead at a meat packing warehouse and wound up being captured by ruthless mobsters. They expect backup to arrive and save them, but it never does. The mob boss shoots Grace in the chest with a shotgun before Danny manages to free himself and subdue them all. He rushes to Grace, who's bleeding out, then outside to radio for help. It's then revealed that no cops responded to his distress call because this event took place on September 11th, 2001, while all available units raced to the Twin Towers. This was also the day that Danny found out he was going to be a father, and we learn that he later named his daughter after his fallen partner.