Our Astrid gets an unexpected visit from her Alternate, while Peter and Olivia track a killer using a toxin that has yet to be invented. Both universes collide in a case that pushes the boundaries of what is possible.
As Rome and Regina continue to move forward with the adoption process, they are thrown into helping Delilah with a troubled Sophie. Meanwhile, Gary confronts Eric about his past, and Eddie pursues a new career in music.
Karen grapples with her feelings as she, Alec and Vivian decide exactly how their relationship is going to work. A bad judgment call involving the kids puts Marc in the doghouse with April, driving her closer to Blair. Joss and Harry rebound from their painful break-up in different ways while Calista enacts revenge on a manipulative Luca.
After Mitch's alter ego, Mr. Duncan, attacks the team's plane then flees, Jamie, Abe and Max (Robin Thomas) set out to find him and help.
The team races to stop the hybrids from breaching the barrier wall by shutting down the last beacon that draws them in.
