Bestselling author Markus Heitz invites readers to an action-packed mystery adventure across three captivating alternate worlds - decide for yourself which world you want to experience first: "DOORS ?", "DOORS !" or "DOORS X"? 3 books, 3 worlds, 3 doors - which will you open? Behind these doors lies much, including adventure. In the cave labyrinth beneath the van Dam villa lurks an ancient secret - behind mysterious doors adorned with enigmatic symbols. When ex-soldier Viktor and his geo-expert team open a door in search of the missing Anna-Lena van Dam, it leads the group into the early medieval 9th century. However, unlike what they know from history books, power is not only wielded by men. While powerful empresses wage war, male conspirators plot the end of the matriarchy. Viktor and his team.