Grover's (Chi McBride) dealings in Chicago with Clay (Mykelti Williamson) come back to haunt him on Friday's episode of Hawaii Five-0, putting his whole family in danger, as well as his relationships with the rest of the Five-0 team.

"Even though [Clay's] not in it, his presence is felt in the episode, because he exposes a backstory that [Grover has] kept hidden from the team since he started," showrunner Peter Lenkov tells TVGuide.com. "You realize that Grover had a life even before Chicago that catches back up with him and puts him on the run, and forces him to really protect his family and not trust anybody, including Five-0."

Catch up on all this week's Mega Buzz!

The backstory pertains to Grover's previous work with the FBI, according to McBride. "Grover has a history with the Federal Bureau of Investigation," he tells TVGuide.com. "He came out of the police academy and the FBI put him on an undercover assignment on a drug family in Philadelphia. And subsequently, he brought that family down, and so it's sort of like a witness protection thing that he's been in, but still in law enforcement. He left Chicago, came to Hawaii, and somehow the information got to some of the surviving members of that family that Grover and his family were in Hawaii, so they're coming for him."

The episode, which features a guest-starring turn from McBride's Human Targetco-star Mark Valley, will introduce us to Grover's son Will. "He has to grow up really quickly this episode," McBride says. "We're on the run from some very, very dangerous people who once ran the Philly black mafia. ... This is basically Will's bar mitzvah in the jungle."

(Full disclosure: TVGuide.com is owned by CBS.)

Crave scoop on your favorite TV shows? E-mail questions to mega_scoop@tvguide.com or drop us a line at Twitter.com/TVGuide.