The HPD system is hacked and the Five-0's confidential informant is murdered. The team enlist the help of the recently imprisoned hacker Aaron Wright to solve the case.
McGarrett and Danny get Tani Rey to join the task force when a hacker manages to let out a dangerous arsonist from prison.
The team investigate the weapon used in the murder of a scuba diver. Analysing the weapon found on the ocean floor they realise it was used in a another recent murder. McGarrett prepares to propose to Catherine.
The stunning truth about a decades-old disappearance of four school boys comes to light when a neurosurgeon is murdered right before a procedure; someone steals McGarrett's car.
When a Russian submarine appears off the coast, the team discover a Russian spy ring hiding in plain sight on Oahu.
