The Clockwork Three by Matthew J. Kirby
Giuseppe is a street musician who works for a cruel employer. If he doesn't bring in enough money, he will not get food or could possibly get thrown into the rat cellar. Giuseppe begins to think his life is hopeless, until one day, he finds a green violin floating in the river.
Frederick is a clockmaker who wants to start his own business instead of being an apprentice. Secretly, his works on making a clockwork man, but he cannot do it alone.
Hannah is a hotel maid, working to keep her family's apartment. Her father is deathly ill and she is their only hope. When she hears of a hidden treasure at the hotel, she knows she must find it to help her family.
All three children are brought together and they realize that they need each other. But can they solve the mysteries before Giuseppe's master finds him, Hannah's father gets worse, or Frederick is caught?