"Arrow" fans will be in for a special treat when Matt Ryan reprises his role as John Constantine on Wednesday night's highly anticipated crossover episode.

In the upcoming episode, which is titled "Haunted," Oliver Queen (Stephen Amell) will call on his old friend John Constantine to help restore Sara Lance's (Caity Lotz) soul and humanity.

As fans may recall, Sara was brought back from the dead when her sister Laurel (Katie Cassidy) used the Lazarus Pit to resurrect her. Sara's life was successfully revived, but she is now suffering from major side effects. It was also revealed that those who are brought back to life through the Lazarus Pits come back with pieces of other souls, inspiring a blood thirst only quenchable by slaughtering the person who killed them. In this case, Sara will target Thea (Willa Holland).

The trailer clip for "Haunted" reveals that John will arrive in Star City on a mission to restore Sara to the person she once was. However, the members of Team Arrow will have different reactions to him. According to executive producer Wendy Mericle, Oliver will be particularly warm to John's arrival.

"Oliver's very welcoming," the showrunner said, according to Entertainment Weekly. She added that Oliver has "a deep well of experience with things that don't make sense and science can't explain, so he's very open to the idea."

Laurel will also be fine with the idea of John showing up to help her sister, but Diggle (David Ramsey) will not be as inviting.

"Laurel just wants her sister back, so she's willing to do whatever it takes, and Diggle will be, not a skeptic, but certainly maybe not as welcoming as Oliver might be," Mericle added.

The EP went on to warn that getting Sara's soul back would be a challenging feat.

"What we typically do in our Act 5 sequence, we have a lot of action," Mericle said. "This is a different way of doing that. Constantine takes them to a different place. They fight, and they get her soul back. It's a pretty cool, interesting, very different sequence for us on the show."

In another preview video, the EP described a feral and murderous Sara loose on the streets.

"We're going to see Sara out in the city doing exactly what we expected of her do, which is randomly murdering people," Mericle explains in the video. "Sara is still being inflicted by the Lazarus Pit side effects, and she's still a wild, feral animal who is determined to kill, and she's unstoppable. It's a very dark episode, where we'll see Laurel really grappling with her decision to bring her sister back from the dead and try to put this genie back in the bottle."

"We're very excited that the only solution for doing that is bringing on John Constantine and he's going to be the key to bringing Sara back and bringing her soul back," the producer added. "We feel very lucky, Constantine is a favorite character of the comic book fans watching our show and it's just a fun, different dynamic to have on the show."

The official synopsis for "Haunted" reads, "When things take a turn for the worse with Sara, Oliver calls in a favor from an old friend who deals in the mystical, John Constantine. John Badham directed the episode written by Brian Ford Sullivan & Oscar Balderrama."

"Arrow" Season 4, Episode 5 will air on Wednesday, Nov. 4 at 8 p.m. ET.

Watch preview videos below.