The 7 Professors of the Far North by John Fardell.
Remember those cool kids' adventures of the 1950s and 1960s? Danny Dunn? Miss Pickerel and her junior sidekicks? The Three Investigators or the Hardy Boys or Rick Brandt or Nancy Drew when she wasn't waffling on about clothes like she does in the new books? Well, bring the format to the present, take three plucky kids (a brother and sister and a boy named Sam with an always useful Swiss Army knife), and get them involved with the kidnapping of six brilliant professors by an unbalanced and meglomaniac former colleague, then mix them with nonstop action, and you have this totally brill novel that you don't have to be a kid to enjoy.
Eleven-year-old Sam Carnabie is facing a boring vacation at his Aunt Roberta's house when his parents let him stay with their old instructor Professor Alexander Ampersand and his young wards, his orphaned niece and nephew Zara and Ben, in Edinburgh. Then one of Ampersand's colleagues shows up with the urgent message "Professor Murdo has returned to Nordbergen." Within a twinkling other colleagues arrive on the scene, then are kidnapped, leaving the kids on their own to mount a rescue.
Fast-paced action takes Sam, Ben and Zara across England, into Europe and then far to the north; meanwhile a mundane teenage girl named Marcia Slick is about to become a victim of her parents' obsessive need for perfection...
Incredible gadgets, adventures on a secret mode of transportation, despicable villains, travel in some of the most incredible vehicles ever, and engaging characters make this one not to miss.