Part of "3 Doctors, 9 Companions" series set in the future, Clara & OC Thirteen / Clara and the Doctor's attempts to live a semi-ordinary life in the futuristic Brighton of 2064 are constantly foiled by old friends, new friends, teenage tearaways, and more timey-wimey, spacey-wacey threats than you can count.

The third and final instalment in the trilogy of 3D9C and 4D12C / Adventures through spacetime are balanced with the domestic lives of the usual cast of mismatched characters while they thwart intergalactic, cross-temporal, supernatural adversaries; everything ranging from killer space-squids to cults to parasitic toilet worms to invisible aliens and much more.

3D9C spin-off set between Chapters 236 and 237. In the chaos of the Prank War, an EMP disables Oswin's hologram and her connection to Clara and sends them both into a dream-like coma full of impossible scenarios and twisted versions of their friends, with the same goal every time of aiding a new Echo while slowly becoming best friends and pseudo-twin sisters.