An action-packed mystery adventure by Germany's Number One bestselling author: choose your adventure when you open DOOR ?, DOOR ! or DOOR X. This omnibus edition includes Doors ? Colony, Doors X Twilight and Doors ! Field of Blood.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 each of the three doors to lead to a different iteration of the world - one in the past, one in the future and one who knows where - but 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?