Episodes
| Episode | Title | First Broadcast | Repeated | Comments |
|---|---|---|---|---|
| 01 | London Below | 20130316 | 20130317 (BBC7) 20130318 (BBC7) 20160221 (BBC7) 20160222 (BBC7) 20131225 (R4) | An act of kindness catapults Richard from his ordinary life into a subterranean world. |
| 02 | Earl's Court | 20130318 | 20130319 (BBC7) 20160222 (BBC7) 20160223 (BBC7) 20131226 (R4) | To learn who killed Door's family, Richard visits a venerable resident of London Below. |
| 03 | The Angel Islington | 20130319 | 20130320 (BBC7) 20160223 (BBC7) 20160224 (BBC7) 20131227 (R4) | Richard and Door travel to the British Museum to locate the citadel of the legendary Angel |
| 04 | The Black Friars | 20130321 | 20130320 (BBC7) 20160224 (BBC7) 20160225 (BBC7) 20131228 (R4) | Richard heads to the monastery where he must undergo a terrifying ordeal to obtain the key |
| 05 | Market Afloat | 20130321 | 20130322 (BBC7) 20160225 (BBC7) 20160226 (BBC7) 20131229 (R4) | Richard and Door find a guide to lead them through the labyrinth deep beneath London. |
| 06 LAST | The Key | 20130322 | 20130323 (BBC7) 20160226 (BBC7) 20160227 (BBC7) 20131230 (R4) | Richard and Door finally discover who ordered the death of Door's family. Can they escape? |