Hawaii Five-O viewers have met Mary, the sister of Steve McGarrett. But they know little about this character, who is played by Taryn Manning.

That will soon change, however, as TV Guide reports a major storyline on the horizon:

In an upcoming episode, Mary will get kidnapped. Through their investigation, McGarrett and Danno will determine that this case is connected to the murder of the former's mother years ago.

And the prime suspect? A businessman with major ties to the Japanese mob... and the governor of Hawaii.

Sounds intriguing. In other Hawaii Five-O news, Mark Dacascos has been cast as a famous villain on the show.

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.