John Allison 
Bad Machinery Vol. 7: The Case of the Forked Road [PDF ebook] 

Time is a fickle creature, especially when there’s wormhole in the science cupboard. When a strange boy who seems far too entranced by cell phones appears, it’s up to Lottie, Shauna, and Mildred to figure out his strange purposes. The Case of the Forked Road, the seventh book in John Allison’s award-winning Bad Machinery series, finds our young sleuths facing the intricacies of time and space itself. What is their science teacher hiding? Who is the mysterious Calvin, why is he dressed like it’s 1960, and why is he obsessed with Communists? And another thing: just what is going on with Jack, Sonny, and Linton?