The 13th Throne #1006959

Some doors only open one way. And some secrets demand to be fed.
Nineteen-year-old Luca Ferretti knows the underground of Rome better than anyone. He and his five friends make their living guiding tourists through the city's forbidden catacombs — until they break through a sealed passage and find something no survey has ever reached. A chamber of dark stone, older than Rome itself. Thirteen thrones arranged around a basin at the centre. Something in the stone has been waiting, with considerable patience, for someone to complete the circle.
The six sit down.
What the chamber gives them is not power in any sense they have a word for. It is something quieter and more permanent: the removal of the small, internal resistance that sits between a person and what they are actually capable of. Each of the six becomes, in their own way, exactly what they always were — only without the friction that kept it human-sized.
The cost is a life. Then another. Then a quiet decision, made together, to keep paying.
As tourists begin disappearing along Rome's most obscure trails, a Carabinieri detective named Serra keeps pulling the same thread — long after his case is reassigned, his file is closed, and he runs out of everything except the one conviction still holding him upright.
The six are still sitting.
The 13th Throne asks a question it refuses to answer cleanly: not whether six people can become monsters, but whether becoming a monster requires losing anything at all.