Eel has troubles of his own: As an orphan and a "mudlark," he spends his days in the filthy River Thames, searching for bits of things to sell. He’s being hunted by Fisheye Bill Tyler, and a nastier man never walked the streets of London. And he’s got a secret that costs him four precious shillings a week to keep safe. But even for Eel, things aren’t so bad until that fateful August day in 1854 - the day the deadly cholera ("blue death") comes to Broad Street.

Everyone believes that cholera is spread through poisonous air. But one man, Dr. John Snow, has a different theory. As the epidemic surges, it’s up to Eel and his best friend, Florrie, to gather evidence to prove Dr. Snow’s theory - before the entire neighborhood is wiped out.