A group of boys and their leaders go on a weekend retreat to an uninhabited island. Not long after their arrival, one of the boys stumbles upon the theft in progress of old World War II bombs. He takes a bullet to the chest. Luckily he survives.
Five-0 races against time to find the bombs before the thief can set them off causing mass casualties. We find out the bombs were paper balloons. They were supposed to be set off to coincide with the Pearl Harbor attack. But for some reason it didn't happen.
As luck would have it, once the team discovers the grandson of the man who was supposed to set them off 75 years ago, they ping his phone, and lo and behold he is in the Five-0 headquarters.
As it turns out, the grandson doesn't have mass destruction on his mind afterall. He just wanted to clear his grandfather's name.
The grandfather had changed his mind about setting them off all those years ago because his love for a local woman was stronger than his love for his country.
Steve's Aunt Deb comes for one last visit. Her husband has died and she wants to give him a proper buriel at sea. She also has a bucket list she wants to finish. She has one item from her husband Leonard's list that wants to finish for him. Poor Steve, he looks a little green around the gills after that one.
Aunt Deb passes away peacefully in her sleep with Steve by her side. She has one last item on her list that she didn't get to finish. Thanks to Steve, Mary and Joanie she gets to cross that one off her list, albiet it is post mortem.