The Conch Bearer (Brotherhood of the Conch) by Chitra Banerjee Divakaruni

In a dingy shack in the less-than-desirable Indian neighborhood he calls home, twelve-year-old Anand is entrusted with a conch shell that possesses mystical powers. His task is to return the shell to its rightful home many hundreds of miles away. Accompanying him are Nisha, a headstrong but resourceful child of the streets, and a mysterious man of indeterminate age and surprising resources named Abadhyatta. His quest will take him farther from home than he's ever been and will teach him more than he ever imagined -- and it will force him to make a poignant decision that will change him forever.