The Doctor and Donna are imprisoned on the Edifice - and become neighbours to a terrifying assortment of aliens. When the TARDIS is invaded by a holographic marketing scam, the Doctor and Donna find themselves trapped on the Edifice, a purpose-built complex of luxury apartments in space. Their new environs leave much to be desired: millions of beings from across the Universe have been gathered to live side by side in similar apartments. Instead of creating neighbourly affection, it's led to terrible battles being waged in the corridors and on the stairwells. The Doctor and Donna must cross the paths of deadly alien mobs as they search for the Edifice's ultimate authority. Who - or what - lies at the heart of the incredible complex? What destructive scourge is eating away at the Edifice itself? And are the Doctor and Donna trapped forever in this living hell?