Amulet Keepers by Michael Northrop

When Alex’s mother uses the Ancient Egyptian Book of the Dead to bring him back from the brink of death, she inadvertently summons a slew of other spirits from the underworld. In Book 2, Alex and his best friend Ren head to London, where people are going missing, treasures are disappearing, and a blood rain is pouring from the skies. Can they stop a powerful Death Walker from destroying the city?