An action-packed mystery adventure by Germany's Number One bestselling author: choose your adventure when you open DOOR ?, DOOR ! or DOOR X

When his beloved only daughter goes missing, millionaire entrepreneur Walter van Dam calls in a team of experts - including free-climbers, a geologist, a parapsychologist, even a medium - to find her . . . for Anna-Lena has disappeared somewhere within a mysterious cave system under the old house the family abandoned years ago. But the rescuers are not the only people on her trail - and there are dangers in the underground labyrinth that no one could ever have foreseen.

In a gigantic cavern the team come across a number of strange doors, three of them marked with enigmatic symbols. Anna-Lena must be behind one of them - but time is running out and they need to choose, quickly. Anna-Lena is no longer the only person at risk.

They little expect door ? to take them back to the 1940s - but this is not the 1940s they know. In this timeline, Nazi Germany capitulated early, the US has taken control of Europe and is threatening the Russian-led Resistance with a nuclear strike. If the team is to rescue Anna-Lena - and survive themselves - they will have to stop this madness - at all costs!

DOORS: THREE DOORS, THREE DIFFERENT ADVENTURES. WHICH DOOR WILL YOU CHOOSE?