Billy believes his friends and family have been replaced by doubles. His psychiatrist believes this is a delusion. Meanwhile, Billy's carrying out an experiment to prove it's no delusion.
| Actor | Role |
|---|---|
 Arthur DarvillBilly | Billy |
| KKate AshmeadDoctor | Doctor |
 Phoebe Waller-BridgeAnna | Anna |
| KKevan BrightingNews Reader (voice) | News Reader (voice) |