A young girl desperately wants to go on holiday somewhere but her family is poor and can't afford it. In an act of naievity and desperation, she spends all her money on stamps and posts herself to her destination through the postal system which is much cheaper.
However, it turns out the postal system is much more complex than she ever imagined and her package gets Lost. She ends up in a world of constant messages and parcels being sent every which way. Within she meets the Lost, others that have travelled through system and got stuck and survive by poaching food parcels. There are stories of people how have escaped the postal system, that vast catacombs of treadmills, scanning machines, parcel shoots, but no-one has ever returned to tell them they've been successful.
The girl has an adventure in the odd, unnatural realm of the Post and together with her new found friends journeys to find a way out, whilst avoiding the darker, nastier denizens of that hidden realm.