Book of Dead follows explorer Rich Wilde through an ancient Egyptian setting, using a 5×3 grid with 10 adjustable paylines built around a single, well-known mechanic: the expanding symbol free spins round. Three or more scatter symbols trigger ten free spins, during which one symbol is randomly selected at the start of the round to become the expanding symbol – whenever it appears during a free spin, it expands to fill the entire reel, which can produce very large wins if it lines up across multiple reels. That symbol stays fixed for the whole round, so once a high-value symbol is chosen, every free spin carries genuine upside. High volatility and a 5000x max win reflect the game’s reliance on the free spins round for its major payouts; the base game itself is comparatively quiet. Book of Dead’s format has since been copied across dozens of “Book of” style titles from other providers, but it remains one of the most-played slots in the genre, helped by Play’n GO’s clean visual execution and a genuinely well-tuned math model behind the expanding symbol mechanic.