Fringe (2008)

S04E11 Making Angels

In this episode, Astrid receives an unforeseen visit from her Alternate, complicating her reality. Meanwhile, Peter and Olivia are on the hunt for a murderer who employs a toxin that hasn't been created yet. As they delve deeper into the investigation, the two universes intersect in a case that challenges the limits of possibility and blurs the lines between their worlds.