The Secret of Indigo Moon — G.P. Taylor

From best-selling author G.P. Taylor comes the highly anticipated second installment of The Dopple Ganger Chronicles, a series that combines art and traditional text to help "reluctant readers" discover the wonder of books.
Erik Morissey Ganger, famed explorer and detective (well, in his dreams), and his mischief-making sidekicks, twins Sadie and Saskia Dopple, didn't go looking for a secret tunnel beneath the school. They never intended to make the acquaintance of a shifty private eye with a nose for trouble. It wasn't part of the plan to come face to face with an old enemy, one with an agenda of his own that could destroy them all. And unraveling the "secret of indigo moon" was the farthest thing from their minds.
At Isambard Dunstan's School for Wayward Children, these things just seem to happen.
In The Secret of Indigo Moon, confirmed troublemakers Erik, Sadie, and Saskia plunge headlong into a new and perilous mystery, one that challenges everything they thought they knew about their lives, themselves, and whom it's safe to trust.