Career U.N. bureaucrat Howard Silk discovers he has a doppelganger in parallel dimension who's about to turn his life upside down.
Prime's effort to stop the assassinations leads him to look to Howard and the killer's double for help.
As Emily Prime makes the crossing to uncover the truth about the assassinations, Prime looks to stay close to Howard as he fights to stop Baldwin's return to the Other Side.
After agreeing to trade places with Prime, Howard discovers some shocking differences in his life on the Other Side.
While posing as Prime gives Howard insight into life on the Other Side - and raises questions about his own - the search for a spy inside OI uncovers new details about the security breach.
As Baldwin confronts Clare with a demand to honour their deal, Prime's investigation into espionage produces an unexpected suspect inside OI.
Groomed from childhood to be a spy inside OI, Clare faces exposure at a crucial point in her mission.
As Howard and Emily Prime learn the truth about Indigo, Quayle struggles with the news that Clare is spying for the Other Side.
As the hunt for the spy forces Prime to go on the run, Howard learns the truth about his wife as the Other Side conspiracy to infiltrate OI unfolds.
As the rogue faction's attack on OI sparks a dangerous diplomatic stalemate, Howard tries to escape the Other Side and reunite with his ailing wife.
While hiding in Howard's life, Howard Prime must avoid detection at home and at the OI. Quayle and Clare struggle to adjust to their new arrangement.
Imprisoned on the Other Side, Howard's must prove his loyalty. Emily Prime gets a promotion.
Howard is transferred to a mysterious prison called Echo. An unexpected visit gives Emily a connection to her old life. Emily Prime and Shaw's investigation is met with resistance.
Howard Prime, Quayle, and Clare must unite against a common enemy. Emily Prime turns her investigation toward her Counterpart. Yanek probes Howard's past.
A new revelation puts Howard Prime and Quayle in jeopardy. Life at Echo is disrupted. Clare reconnects with her past.
In 1987, an accident at a top secret lab opens a wormhole between parallel worlds that brings East German scientist Yanek Tomes face-to-face with his doppelganger on the Other Side.
As the Other Side looks to start negotiations to reopen the Crossing, Temple questions Quayle's ability to investigate Indigo. Clare is drawn into helping some old friends, while Howard and Emily Prime look for answers at Echo.
Howard Prime and Emily work together to figure out Indigo's plans. Clare and Quayle consider their future. Howard must face the truth about his wife.
As Emily Prime prepares to make good on her deal for Howard's release, Temple enlists Clare to expose the Indigo sleeper cell before they unleash their attack.
As Mira unveils the last act of Indigo's revenge plan, Howard and Emily set out to repair their marriage. The truth about Clare and Spencer haunts Quayle.