The episode opened with a school bus full of children and a few adult chaperones, which was immediately taken hostage. Five-0, fresh from a press conference with the governor after they intercepted and seized $80 million in cocaine that was being smuggled into Honolulu, were immediately called to save the schoolchildren who are being ransomed for the swift return of the seized cocaine.
It seemed that there were no leads other than the man they have in custody from the drug bust, who goes by the name Vargas. He is claiming to know nothing other than the name of the drug cartel's head honcho is Hugo Castillo.
As the clock ticks down it leaves the governor no other choice than to essentially meet their demands and drop off the drugs in exchange for the kids. but upon dropping off the drugs, Steve barely escaped an explosion in the van in which they are left, destroying the drugs.
When Five-O learns one of the kids recognized one of the hijackers as an acquaintance of his father's, they ended up with a solid lead as it turned out that the father was essentially Hugo Castillo "landlord" as he was renting Castillo a warehouse. The father decided to try and take matters into his own hands and end the kidnapping without police assistance. However Five-O turned up on the scene saving the father, and all the kids.