Two devious villains are returning for the season finale of "Hawaii Five-0."

Wo Fat (Mark Dacascos) and Nick Jonas' Ian Wright are returning for the finale of the fourth season, which is titled "O ka Pili 'Ohana ka 'Oi," (Family Comes First).

In the episode, McGarrett (Alex O' Loughlin) and Captain Grover (Chi McBride) will team up to rescue Grover's daughter when she's kidnapped by Wright.

"[Grover] starts off the season looking at what McGarrett's doing as being unorthodox, and it's everything he hates in a cop," executive producer Peter M. Lenkov said, according to TV Guide.

"Now, Grover's put into a situation where he's got to act the same way. I think he sort of learns a lot about himself and gains a new respect for McGarrett."

Wo Fat will also break free from prison and head back to the tropics.

"The end is going to be a big shocker," Lenkov teased. "And I don't think anybody is going to see it coming."

On the last episode before the show's brief hiatus, Danny and McGarrett got caught in a major explosion.

In "Ku l Ka Pili Koko," (Blood Brothers), the Five-0 and SWAT teams go to a location where an illegal weapon exchange is supposedly taking place. The teams find nothing and decide to leave.

Just as Danny (Scott Caan) and McGarrett are about to leave, McGarrett hears a ringing sound. The pair open a back door at the parking garage and find a man gagged and tied. They remove the man's cell phone from his pocket and take his gag off. The man says "bomb," and seconds later, the building explodes, trapping McGarrett and Danny inside.

Hours earlier, McGarett gets a phone call from Halawa Prison, where Jason Decker asked to see him and Danny.

Decker tells them he wants a deal: He wants to be put in a minimum security prison and also wants his sentence cut in half. He uses important information as leverage. He tells them that a gun supplier in the Philippines is bringing an illegal gun shipment in an hour.

Back at the exploded building, McGarrett regains consciousness and looks for Danny. Danny is injured and trapped underneath rubble and large rocks.

They decide to make noise in the hopes that someone will hear them. Five-0 is on the scene looking for them, and Catherine (Michelle Borth) hears them. She calls McGarrett's cell phone, and McGarrett tells her their location. Catherine arranges a video call with them to find out their location and captures a photo of the man who was tied up, who is now dead.

Danny finds anticoagulant pills in the deceased man's pocket in addition to a scar, meaning he most likely had surgery recently.

The Five-0 team checks local hospitals and DMVs. They find a file on Marcus Decker, Jason Decker's younger brother. They find out Jason Decker has been working with the ATF for months and that someone decided to kill his younger brother for revenge. Chin (Daniel Dae Kim) and Kono (Grace Park) speak to Jason, and he says that a man in his cell block named Spider gave him the intel.

Decker tells Chin and Kono that Spider paid him $5,000 and promised him $20,000 more if he would get Five-0 to the garage.

Meanwhile, at the building, Danny and McGarrett suffer another cave-in and lose cell phone reception. McGarrett then comes up with an idea to use a grenade and a pipe to blow their way out. It's successful, and the two are rescued.

Once they are outside, Chin tells McGarrett that a burner phone has been traced back to Edward Cobb, an ex-CIA agent who used to run Black Ops out of Southeast Asia in the 1970s. McGarrett then realizes that the explosion is about his mother.

McGarrett calls Cobb on the phone then goes to his office to force him to divulge who's in the grave in Cambodia. He said it is Wo Fat's mother, who was accidentally killed when Wo Fat's father was targeted, and that Wo Fat's father is still alive.

Cobb then goes to shoot McGarrett, but McGarrett is able to shoot and kill him before Cobb is able to get his gun.

On the next episode, "Pe'epe'e Kãnaka," "As Five-0 investigate the death of a pool cleaner, they uncover a group of radicalized students who may be plotting a terrorist attack on U.S. soil."

Watch the promo below for the next episode, which airs Friday, April 25 at 9 p.m. EDT on CBS.