NB! SPOILERS ON THE WAY.
The fourth season features the episodes "USS Callister", "Arkangel", "Crocodile", "Hang the DJ", "Metalhead" and "Black Museum". In particular, there are two basic themes that have been permanently fixed in this season – themes that have also been consistent in season after season, and often in several episodes in each round. One concerns fables that raise themes around new possibilities for monitoring and control (previously brilliantly treated in "White Christmas" (S2), and now in "USS Callister"). The second theme is the generic opportunities for digital duplication of identities (in "Hang The DJ" and "Black Museum"), with virtual, digital post / parallel life as the favorite field. If we include one-to-one simulations where the system directly connects to the client's brain or digitally sampled DNA recreates selected real-time experiences of life on the top shelf, we have covered almost half of the episodes.
It is in the nature of things that all repetitions must have something Nietzschean. . .