A hilarious new story with fabulous pictures by an internationally acclaimed illustrator. Captain Quack and his loveable yak deliver the post to the mountains and back. At least, that's the idea. But Yak loses all the post, and keeps picking up friends instead. Stranded baa-lambs; lost chickens; even some hitch-hiking rabbits - Yak stacks them all up on his back, till he surely can't carry any more. Or can he? Join Quack and Yak on their brilliantly bonkers journey, and find out just how much you can stack on the back of a yak.