In an upcoming episode of "Hawaii Five-0," the bureau will see the return of the notorious serial killer Dr. Madison Gray (Elisabeth Rohm).

Although Steve McGarrett (Alex O'Loughlin) and Danny Williams (Scott Caan) had a pretty smooth Valentine's Day, what is to come will frazzle the minds of the detectives, when a serial killer initiates mind games with them.

As revealed in the synopsis for "Hawaii Five-O" season 7 episode 17, titled "Hahai I na pilikua nui," or "Hunting Monsters," Dr. Gray stumbles into the Honolulu Police Department, claiming she has amnesia. With that in mind, she claims to have no knowledge of the blood that she is covered in, which will match that of Alicia Brown's (Claire Forlani).

In the forthcoming episode, McGarrett and the team will be getting to the bottom of their latest case, and will attempt to unravel the twisted mind of Dr. Gray. More importantly, they will have to find out if Brown is still alive, and, if she is, they will have to find out where she is being held captive before it is too late.

With the return of the guest stars, the series is expected to have an altered case-of-the-week format. Also, the return of the recurring cast members will add a few plot twists to the current season.

To recap the Valentine's Day special, McGarrett and Williams attempted to spend a romantic holiday with their respective girlfriends, while the rest of the team was tasked to solve a case about Jeremy Holder, the man who was found dead in a dumpster.

Dr. Gray was first introduced in an episode called "He Moho Hou" or "New Player," wherein she was still serving as a police psychiatrist.

"Hawaii Five-O" season 7 episode 17, titled "Hahai I na pilikua nui," or "Hunting Monsters," premieres on Friday, Feb. 17, at 9 p.m. EST on CBS.