With Rachel's father, Trigon, having successfully turned Dick dark, he sets out to win the others over to his side by embracing their inner darkness. With everyone under Trigon's control, Rachel and Gar find themselves fighting what seems like a hopeless battle against the powers of Trigon.
While Dick trains the next generation of Titans, Donna and Kory track down a rogue metahuman. But an old threat drives the Titans - old and new - back together.
With the reemergence of Dr. Light, the old Titans reluctantly return to Titans Tower to strategize against their old enemy. But the secrets of the Titans' past threaten to tear apart this newly formed team from within. While the old Titans question Dick's acceptance of Rose Wilson into their midst, the new Titans start to wonder about the unspoken tragedy that disbanded the group years before. Meanwhile, an old friend from Kory's home planet of Tamaran comes to Earth with an urgent mission.
Four years ago, Dick, Donna, Hank, Dawn and Garth aka Aqualad are living together in Titans Tower, thriving as a superhero team, and growing into a tight-knit family. But their personal feelings start to bleed more and more into their work, and with the arrival of a new villain, the Titans begin to question their destiny as heroes.
With the team in upheaval, the Titans do everything in their power to save Jason's life. But when Deathstroke demands they turn over Rose, the dilemma threatens to tear the team apart.
Conner Kent and Krypto escape from Cadmus Labs. His search for the truth about his past leads him to Lionel Luthor and genetic scientist Dr. Eve Watson.
Tensions are running high at Titans Tower after their most recent encounter with Deathstroke. Kory attempts to learn more about Conner Kent, and Rose tries to help Jason cope with his near-death experience, while the old Titans keep getting mysterious reminders of a past they'd rather forget. As Dick sets out alone to track down Deathstroke, a familiar voice begins to haunt him - taunting him and attempting to guide him back to being the leader the Titans need. With all the strange ongoing happenings and Dick's continuing to keep the team in the dark, both Jason and the Titans reach a potential breaking point.
Dick finally reveals the truth to the team and, in flashback, we learn the secret behind Deathstroke's vendetta against the Titans. After the hug of Garth, Dick, Donna, Dawn and Hank befriend Jericho Wilson, Deathstroke's son. Realizing that Slade's devotion to his son might be Deathstroke's only weakness, Dick is eager to use the information against his nemesis. But as the Titans' friendship with Jericho grows, and he's taken into the fold, Dick is forced to make a choice between loyalty and revenge.
In the aftermath of Dick's confession, the Titans' world is rocked to the core - and Dick's fear that his secret would break up the Titans comes true. Abandoning Titans Tower, the heroes all go their separate ways. Hank and Dawn return to Wyoming, Jason and Rose leave together, and Donna agrees to take Rachel with her. Kory, meanwhile, is surprised to hear from Faddei, who's returned with bad news from her home planet. Leaving Gar alone to tend to the still wounded Conner, Dick departs as well, in search of absolution for Jericho's death.
Gar finds himself caught in the crossfire. Dick's hero side has not been buried forever. Rachel meets a runaway girl.
With Dick still in prison and Gar under the microscope at Cadmus, the remaining Titans are called together to save their teammates.
Finding himself at a new low, Hank is cage-fighting for money to support his unhealthy habits. But when he wakes to find his Hawk suit gone - and an imposter acting in his stead - he realizes how far he's fallen... & it's time to make a decision. Meanwhile, Donna and Dawn confront a Cadmus operative to gain information about Gar and Conner, as Cadmus initiates its Phase One plan, tapping into Gar's lethal abilities. Back in Gotham, Rose is overcome with guilt and reveals her secret to Jason. When Dick realizes that Jericho might have somehow survived his death at his father's hands, he escapes from jail in the hopes to rescue him. But first he'll need a new suit to replace the Robin suit he destroyed.
The Titans reassemble under Dick, who has now fully taken on the mantle of Nightwing, to fight Deathstroke and attempt to save Jericho. But that's not the only struggle they face - as the team finds themselves up against mind-altered versions of Gar and Conner, who are now supercharged weapons at the "mercy" of Mercy Graves and her Cadmus final Phase Two plan.