Deep Secret is a fantasy novel by Diana Wynne Jones, published by Gollancz in 1997.

[1] The book's first narrator is Rupert Venables, the junior "magid" responsible for Earth and the Koryfonic Empire, a collection of Ayewards worlds.

Venables draws the candidates for Earth senior magid together in an unlikely place: a science fiction convention in the town of Wantchester.

Pleas for help from the unsettled Koryfonic Empire force Venables to cross over to the Ayewards world Thule to seek help from his magid brother Will.

Maree and Nick unwittingly follow him through the gaps between worlds, nearly killing themselves in the process.