Book of Fire

What "Book of Fire" actually refers to

Merkur Gaming sells the European way: a cabinet ships with a mix of dozens of titles behind one menu, and the operator licenses the pack rather than the individual game. So this entry is a game inside a mix, not a machine you will find standing alone on a floor.

That matters for payback. The theoretical return is configured per game per installation, and operators in most European jurisdictions choose from a set of approved percentages. Manufacturers ship the same title in multiple par versions — commonly spanning roughly 85% to 96% across the industry — and nothing on the machine tells you which one you are sitting at.

Numbers you find quoted for this title elsewhere are almost certainly from its online version, which is a separate product with its own certified maths and typically a higher published return.