The Doctor (Jodie Whittaker) and her companions Graham (Bradley Walsh), Ryan (Tosin Cole), and Yasmin (Mandip Gill) arrive in Norway at the present time. Living in a cabin nearby is a blind teenager named Hanne (Ellie Wallwork) who lives with her father Erik (Christian Rubeck) since her mother Trine (Lisa Stokke) died. Now, her father has disappeared. She hears a creature outside the cabin every day. Upstairs, there is a mirror with no reflection, which they believe is a portal. The Doctor, Graham, and Yasmin enter it, but Ryan remains behind with Hanne and discovers speakers around the house that keep her inside with scary sounds. Hanne knocks him out and enters the portal.
The Doctor and the others are in the Antizone, a buffer-space between universes. An alien named Ribbons (Kevin Eldon) guides them through the zone. When he tries to take the Doctor’s sonic screwdriver, he is killed by flesh-eating moths. The others flee through another portal into a reflected parallel universe in which they find Erik talking to Trine, even though she is dead. Graham is talking to his dead wife, Grace (Sharon D. Clarke). The Doctor thinks this is because of the Solitract, a sentient entity who is a universe seeking companionship. Hanne arrives and recognizes the Solitract Trine as an imposter and it is ejected into the Antizone.
The Doctor realizes that the Solitract is collapsing in on itself because of all the beings around. She offers to take everyone away in exchange for herself, desirable to the Solitract because of her great experience. The Solitract ejects Erik and brings the Doctor to a white space. It assumes the form of a talking frog with Grace’s voice, but the Doctor says they cannot co-exist. The Solitract releases her through the Antizone and the portals collapse. Erik decides to return to Oslo with Hanne and Ryan bonds with Graham, calling him Grandad.
The episode was written by Ed Hime and directed by Jamie Childs. It was well-received as somewhat incongruent but presenting a compelling meditation on grief and guilt. Ellie Wallwork (Hane) is a blind actress. Hanne and Erik are real father and daughter. The Doctor says she had seven grandmothers. Graham keeps a cheese and pickle sandwich for emergencies. All the scenes in the Solitract were edited to depict a mirror image.