In the murky waters of the Thames, where London's secrets lie buried for centuries, three mudlarkers make a discovery that will change their lives forever. Emma Carter, Jake Morrison, and Oliver Chen unearth an ornate medieval reliquary during a routine morning search along the foreshore. The exquisitely crafted box, untouched since the Great Fire of London in 1666, promises to be the find of their careers. But their excitement soon turns to dread as all three begin experiencing mysterious symptoms—rashes that form ancient patterns, vivid dreams of medieval battles, and a progressive illness that baffles modern medicine. As their condition worsens, they make a shocking discovery: the reliquary contains human remains and documents revealing it belonged to Sir Edmund Blackwood, a Crusader knight who died protecting a sacred relic in the Holy Land. Racing against time as the mysterious affliction threatens their lives, the trio must unravel the knight's story and discover why the reliquary was stolen during the Great Fire, only to be cast into the Thames by terrified thieves. Their quest leads them through London's most prestigious museums and libraries, into forgotten archives, and finally to the ruins of Blackwood Castle in Northern England, where an enigmatic groundskeeper seems to know more about their discovery than should be possible. As Emma, Jake, and Oliver piece together a tale of honor, betrayal, and an oath that transcends death itself, they realize that some treasures aren't meant to be found—they're meant to be returned. With only days left before the curse claims them, they must discover where Sir Edmund's remains truly belong and uncover the truth behind a guardian who has waited centuries for someone to finally bring him home.