A dark secret resurfaces when Jenna Cavanaugh returns to Rosewood; the girls deal with questions surrounding Alison's death.
The team look into the death of a man dressed as a Hawaiian NaKoa warrior, after his body is found near the site of a war re-enactment.
The bodies of two serial killers are found with chess pieces in their mouths, so the team hunt for the vigilante as fear grows that tourists aren't safe in Hawaii.
A rogue MI-6 agent is the key to finding a terrorist who plans to cause the meltdown of nuclear reactors across Europe. McGarrett and Danny need the help of an FBI profiler to find a killer.
New clients hire Magnum and Higgins to find their missing brother, which results in Higgins getting shot and TC abducted; Higgins and Magnum are surprised when her surgeon asks her out.