TUNNEL AT WORLD’S END is a fantasy adventure written for young children. It comprises fourteen chapters and is about 43,000 words long .

Stephen, Mary and Pamela spend Christmas in Scotland. They tell their sceptical cousin Toby about their earlier adventure in Within. To try to prove it really happened, they look for the pine cone they brought back and planted in summer, only to find it has already grown into a tree.

The Sage unexpectedly uses the existence of the tree to call all four children into Within. He tells them that the spell protecting Within from the half-men has not been fully restored. Strangers to Within are needed to brave the spells at the Tunnel at World’s End, where the half-men spell can be found and repaired.

The magicians Jasmi and Micon gather together companions for the expedition, and tell the children about the mysterious prophecy which seems to describe them and their journey. Micon gives them a key which will open a door at World’s End – but he warns them that there are two identical doors. One of them will lead to the spell. Opening the wrong one will lead to the destruction of Within.

They leave the island with the help of a giant, and set sail again. They narrowly avoid being drawn into an area called the Maelstrom, and eventually land in Far Beyond, where they are attacked by half-men. They escape down a narrow gully, only to be trapped there by a dragon. Jasmi gets them safely past by using a concealing spell, leaving the dragon to deal with the pursuing half-men.

Toby is separated from the others in the Burnt Forest and is almost caught by a Mutterer (a creature also described in Search for the Sage) before being rescued. Immediately afterwards, Jasmi calls an Occupyx from the lake to deal with another swarm of half-men, allowing the expedition to get away.

At the Double Mountain (where a mountain reaching down from Topside meets one reaching up from Far Beyond), Jasmi and the elf Varrilan deliberately let themselves be chased by half-men. This leaves the way to the Tunnel free for the children.

They pass through the various tests foretold by the old prophecy – including the one where they must decide which door to open – and finally Mary’s tears restore the half-men spell to its full strength. The children are then taken back to the coast, where they meet the Sage. He tells them that now they have fulfilled their purpose in Within, they have to return to their own world, otherwise they would start using up Within’s pool of magic again. So he returns them back to their Christmas in Scotland.