The Cure-All Kid. The Young Healers Mysteries

Larkspur Hollow, 1907. Twelve-year-old Jasper Quill sweeps floors and mixes powders for the town apothecary, Mr. Doyle, and has a gift for noticing what other people miss - a wheeze before a cough, a twitch before a headache, the tiny tell that means someone's fibbing. When a dazzling traveling medicine show rolls into town with a wagon painted gold and a silver-tongued showman named Dr. Marvel Cassidy, promising his Miracle Elixir cures everything from earache to rheumatism to the common cold, the whole town lines up with their nickels.
But Jasper notices something wrong: the children who take the tonic don't get better - they get strange. Sleepy. Sluggish. Worse. Armed with his first aid know-how, a sharp eye, a sharper ear, and a growing stack of clues, Jasper sets out to prove that the "miracle" in the bottle is really a secret ingredient nobody's supposed to know about - before Dr. Marvel packs up his wagon and rolls out of town with the evidence, and the truth, right behind him.
A rollicking turn-of-the-century mystery about quack cures, real medicine, and the courage to call a fraud a fraud.