<i>Ding Dong!</i><br><br>The TARDIS is invaded. A plea for help delivered by robot summons the Doctor and her friends Yaz, Graham and Ryan to <i>Kerblam</i> - 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.<br><br>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...?