A group of boys go on a retreat to an uninhabited island with their leader to learn about the old ways. One of them stumbles upon some old bombs from World War II being stolen and he is shot. Luckily the boy survives a bullet to the chest.

Five-0 races to find the bombs before the thief can set them off and kill innocent people. We find out they are paper balloon bombs that 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 they discover the grandson of the man who was supposed to set them off 75 years ago is the culprit, they ping his phone and he just so happens to be inside Five-0 headquarters.

It turns out he doesn't have mass destruction on his mind and just wants to clear his beloved grandfather's name. The grandfather had changed his mind all those years ago, because his love for a local woman was stronger than his love for his country. 

Also Steve's Aunt Deb comes for a visit. Her husband Leonard has died and she wants his ashes taken out to sea. Aunt Deb also has a bucket list. One of the items is from Leonard's list that he didn't get to do. So Aunt Deb completes it for him and just about makes Steve lose his breakfast in the process. She gets to cross a few more things off her list.

Aunt Deb passes away peacefully with Steve at her bedside. She has one item left on her list that she didn't get to do, climb a really tall mountain. Which thanks to Steve, Mary and Joanie, she gets to do post mortem.