The episode opened with Steve sister, Mary showing up to surprise him with the announcement that she was working for an airline that would bring her to Hawaii twice a week.
The next day Steve got a call that his sister had been arrested for attempting to smuggle 20 million dollar in diamonds to New Year taped to her body. Steve and Five-0 began checking out her story that she was threatened to do it.
Mary's story checked out, her friend and co-worker Angela was shown being kidnapped by a tall dark-skinned man. After Five-0 request the diamonds to be transported to headquarters the truck carrying them was intercepted and two officers died when the diamonds were stolen.
This brought Captain Fryer into the picture who knew a guy that could tell them who was fencing the diamonds, a former thief named August March. August March served 30 years for fencing stolen goods and was recently paroled.
August was able to identify the diamond; this led Five-0 to the man who supposedly kidnapped Angela where they found out it had all been faked. After charging an ex-cop, now felon with the death of the two cops, because he arranged the theft, Five-0 celebrated Steve's birthday.
August ended up meeting Angela to pay her for the diamonds but instead killed her and took the money and the diamonds.