From BBC America:

After evading a Neolution attack in Iceland, Sarah returns home to track down an elusive new ally. She follows breadcrumbs and uncovers the next facet of Neolution’s agenda – implanting dangerous technological devices in humans. However, those she left behind are wary about her return, not wanting to relinquish their semblance of normalcy. As Cosima struggles with Delphine’s disappearance, Alison and Donnie host a pregnant and ever-hungry Helena. Meanwhile Felix, feeling like an outsider, embarks on his own journey of self-discovery.