The Sinister Substitute — Wendelin Van Draanen

Dave's most despised teacher, a gleeful frog dissector named Ms. Veronica Krockle, is absent. Her students are psyched! But Sticky is suspicious. Especially when the substitute teacher turns out to be strangely interested in geckos. Or rather, boys with pet geckos.

That's no substitute! That's Damien Black, dastardly treasure hunter and master of disguise!

If Damien Black is in school, does that mean he's behind Ms. Krockle's absence? Could she have been kidnapped? And does that mean Dave has to rescue her? Ay chihuahua! The capped crusader is (reluctantly) on the case.