An armored truck was high jacked and all but one of the guards was murdered at the opening of the episode. The Five-O were called in to investigate and immediately started to track the money from the truck. Unfortunately, the robbers dumped the truck and the money in the ocean and left the team wondering what the thieves' true goals were.
One of the armored truck guards remained alive but in critical condition at the hospital. Danno and McGarrett had hoped to speak to the guard once he was conscious, but he was attacked once he came to and was sent back into a brief coma. McGarrett and Danno were unable to stop the perpetrator who slipped expertly out of their grasp.
A review of the robbery revealed that the robbers used clones to mask their intentions. An ad they placed on the internet for a fake painting job led the Five-O to a chiropractic office that was being used as a doping center while the doctor was away on vacation. A print on one of the bags of blood used for the doping, led to a suspect that pointed the way to the true robbers who were going to use a triathlon to gain entry to their actual target.
The house the thieves were using to train and coordinate their robbery in happened to be right next door to Danno's ex-wife Rachel's house. Rachel reluctantly agreed to allow Danno and McGarret to enter the house and use it to set up surveillance on the thieves. Rachel even helped to get Danno out of a tight spot when two of the robbers returned to the house while Danno was inside searching for clues.
On the day of the triathlon the Five-O kept careful surveillance on the tracking devices used to keep tabs on triathlon competitors during the race, but found the thieves had placed the devices on the bikes of other athletes. Using the data from the black box on the armored car the team chased the thieves down to a diamond importer and quickly caught up with, and arrested all four along the planned escape routes that Chin and Kono had surveilled the night before.