John Allison 
Bad Machinery Vol. 3: The Case of the Simple Soul [PDF ebook] 

The Tackleford gang is back with a new case that demands solving! When Tackleford’s derelict barns begin going up in flames, Linton and Sonny are on the case with a moderately mysterious new friend. Paths cross, however, when Lottie and Mildred meet a terrifying yet misunderstood creature living beneath a bridge! Throw in an overly enthusiastic Fire Brigade, a transforming skate ramp, and a new French teacher and you’ve got the kind of charming genius that can only be found in John Allison’s BAD MACHINERY.