Happenstance Found (Books of Umber Series #1)

Twelve-year-old Happenstance awakens in a cave with no memory of who he is or how he came to be there. Soon a mysterious trio arrives to take him away: the explorer Umber, the shy archer Sophie, and Oates, whose strength and honesty are both brutal. Hap and his new acquaintances narrowly escape the cavernous underworld and make their way to Lord Umber's bustling jewel of a harbor city, Kurahaven.

Once there, Hap learns that Lord Umber is an extraordinary man -- he's a merchant, adventurer...