The Flash
"The Flash" Season 4, episode 15 saw "Arrow" character John Diggle (David Ramsey, left) cross over to team up with Barry Allen (Grant Gustin, right) against a new meta-human. The CW

It was an eventful week for the CW's "The Flash" in Season 2, episode 15, "King Shark." At long last, the identity of the hero's greatest enemy is revealed, as a friend from "Arrow" comes to town on a meta-human hunt.

The episode opens right where last week’s left off, in the very emotional aftermath of Jay Garrick’s (Teddy Sears) death at the hands of Zoom. The villain sucked Garrick’s body back through the portal to Earth-2 before it closed forever. Although they successfully rescued Harrison Wells’ (Tom Cavanagh) daughter, Jesse (Violett Beane), they felt dejected by their inability to stop the villain now that there’s no way for them to travel between dimensions.

It quickly becomes clear that the only thing they can do to cope with their loss is bury themselves into their work and move on. Those that returned from Earth-2 agreed never to speak to the others about what happened there, for fear that it would change the natural course of the world. Just when everyone’s emotions are about to boil over, a mutual enemy swims into town to unite them.

The episode cuts from Central City to an A.R.G.U.S. prison that’s playing home to King Shark, the half-man-half-shark monster that attacked Barry earlier in Season 2. Just as “Arrow” character John Diggle (David Ramsey) is visiting his wife, and the head of A.R.G.U.S., Lyla (Audrey Marie Anderson), King Shark escapes and heads in the direction of Central City.

Meanwhile, Barry (Grant Gustin) and Cisco (Carlos Valdes) are noticing that Caitlin (Danielle Panabaker) has been rather cold since they returned from Earth-2. This strikes a particular nerve as it was revealed that her doppelganger in the parallel dimension turned into DC Comics villain Killer Frost. Before they can reach a conclusion on the matter, Diggle and Lyla show up to tell them that King Shark hasn’t forgotten his Zoom-imposed mission to kill him. They tell the hero as a courtesy, but insist that A.R.G.U.S. has the situation handled. However, Barry says he owes it to Jay to rid Earth-1 of the last of Zoom’s attackers.

Meanwhile, Joe (Jesse L. Martin) and Iris (Candice Patton), want Barry to start getting along with Joe’s newly -discovered son, Wally West (Keiynan Lonsdale). Ever since Wally decided to let Joe be a part of his life, he’s remained really distant to Barry, prompting the hero to wonder if Wally has a problem with him. In order to help, Joe enlists Barry’s help on Wally’s engineering project. With King Shark quiet for the time being, Barry agrees to come over and take a look.

The Flash
"The Flash" Season 2, episode 15 saw "Arrow" character John Diggle (David Ramsey, right) team up with Barry Allen (Grant Gustin, left) in order to stop a killer meta-human attack. The CW

Wally has designed a turbine-powered jet engine for a car, but Barry’s initial reaction isn’t too supportive. The two exchange words and Wally admits that he’s upset at how much the family that he feels abandoned him loves this stranger that they raised. Just when he’s about to storm out, King Shark makes his appearance in Central City by tearing through the roof and demanding to see The Flash. Joe steps in to distract the monster with his sidearm, giving Barry a window to suit up and call King Shark to the street. He engages the villain but quickly gets knocked into the side of a car. Before the meta-human can move in for the kill, Diggle and Lyla arrive and chase him back to the water.

When Barry gets back to the house, Wally accuses him of hiding upstairs and being a coward. After Wally finally leaves, Barry tells the others that he deserves the way Wally is treating him because he’s not perfect. With that, Joe sits Barry down for a frank discussion and asks him what happened on Earth-2. Unable to contain it any longer, he tells Joe and Iris everything about him being responsible for Joe’s death on the parallel world.

The next day, the team develops a way to lure King Shark to a decoy Flash that A.R.G.U.S. can then use to lure him into a prison transport. Unfortunately, when they put the plan into action at the Central City docks, the trap doesn’t work. This forces Barry to engage the beast on the open water, where he has the advantage. In an act of quick thinking that only Barry Allen is capable of, he runs in a circle around King Shark, trapping him in a vortex of water and electricity. Using a move that honored his friend’s memory, Barry knocks the villain out by using the lightning-throwing technique Jay Garrick taught him before he died. With the target in custody, Diggle says goodbye to Barry. Before he goes home to Star City, he warns him of the danger of letting the death of a fellow soldier overtake him with guilt.

A newly invigorated Barry gathers the team together at S.T.A.R. Labs the next day to declare that their new mission is to find a way to re-open the portal to Earth-2, track down Zoom and finally defeat him once and for all. That’s when the episode shifted to its biggest shocker of the night, and possibly the history of the series. Back on Earth-2, Zoom brings the body of Jay Garrick back to his holding cell and presents it to his masked prisoner. When he does, he finally removes his mask and reveals himself to be Hunter Zolomon, his Earth-1 doppelganger. The episode ends with the newly unmasked villain suggesting that the death of Garrick is going to be a problem for his yet-unknown plans.