Mike accompanies Sue on a college tour weekend, and Frankie abandons Brick with a school project and a revolving door of babysitters while she goes to see Axl play in his first college football game.

Oliver, Arsenal and Diggle track down the location of a boomerang-wielding killer named Digger Harkness, but are surprised when they come face to face with an A.R.G.U.S. team. Diggle asks Lyla why A.R.G.U.S. is involved but she defers until Harkness attacks the building, killing several agents and targeting Lyla. The Arrow joins the fight and gets help from an old friend — The Flash. Harkness manages to get away and Oliver teams up with Barry again to find him before he can get to Lyla. When Harkness plants five bombs in the city that are timed to explode at the same time, both teams must come together to save the city.

Oliver, Arsenal and Diggle track down the location of a boomerang-wielding killer named Digger Harkness, but are surprised when they come face to face with an A.R.G.U.S. team. Diggle asks Lyla why A.R.G.U.S. is involved but she defers until Harkness attacks the building, killing several agents and targeting Lyla. The Arrow joins the fight and gets help from an old friend — The Flash. Harkness manages to get away and Oliver teams up with Barry again to find him before he can get to Lyla. When Harkness plants five bombs in the city that are timed to explode at the same time, both teams must come together to save the city.

SHIELD discovers the ancient city before Hydra, but uncovering the secrets may require one of Coulson’s team to make the ultimate sacrifice. Meanwhile, May and Skye race to get to Raina before Whitehall takes her.

Eliza’s effort to “follow through” on a work idea impacts her relationship with Freddy. Henry rejects an admirer, leading to unexpected consequences.

Barry is thrilled when Oliver, Felicity and Diggle come to Central City to investigate a case involving a deadly boomerang.

When the star of Castle’s favorite ‘80’s action movie is mysteriously murdered, Castle and Beckett delve into the victim’s secret past and pursue his killer with help from a team of aging action heroes.

Jane and Lisbon begin their new relationship, but they must hide their feelings for each other from their colleagues as they investigate the murder of an undercover agent. Also, young, ambitious agent Michelle Vega joins the team.

For his fortieth birthday, Henry requests that Eliza find him a meaningful gift, but when she buys him tickets to see his favorite band, it creates tension between Henry and Julia, the woman he’s seeing.

The Flash goes up against Farooq aka Blackout, a metahuman who can harness electricity. During their battle, Farooq zaps The Flash and siphons all his electricity, leaving The Flash without his speed. Dr. Wells, Caitlin and Cisco work to reverse the effects on Barry, but their efforts are disrupted when Farooq comes banging on S.T.A.R. Labs doors in search of Wells, who he blames for his accident. Without Barry’s powers to protect them, the group must figure out a way to save themselves from the metahuman. Meanwhile, Tockman manages a coup inside the Central City police department and takes several people hostage, including Joe and Iris. While Iris is sure The Flash will save them, Eddie has a trick up his sleeve.