The Great Trouble: A Mystery of London, the Blue Death, and a Boy Called Eel by Deborah Hopkinson

It's 1854; Eel, an orphan, spends his days by the River Thames searching for things to sell and avoiding Fisheye Bill Tyler. The Great Trouble begins one fateful August day when it's clear that cholera has come to London. The deadly epidemic spreads, and before the entire neighborhood is infected, Eel and his friend Florrie must gather evidence that will prove Dr. Snow's theory about the disease.