Ding Dong!

The TARDIS is invaded. A plea for help delivered by robot summons the Doctor and her friends Yaz, Graham and Ryan to Kerblam - the biggest retailer in the galaxy. Posing as new recruits among the thousands of human workers, the TARDIS crew uncover a deadly plot that threatens the life of every person in the warehouse - and beyond.

Who has sent for the Doctor? What is the dark secret at the heart of Kerblam's operations? And who will escape the merciless Postmen...?