The Mystery of the Disappearing Dogs, by Arthur Hammond (epub/Kindle/pdf)$2.99
When Sputnik, mascot of the Annex Gang, was lost in downtown Toronto, the gang blamed their rivals, the Spadina Gang. It turned out, though, that the Spadinas had lost their dog, too. In fact dozens of dogs were missing all over the city.
When the kids learned that Sputnik and the other dogs might have been stolen for sale to a research institution that used animals in experiments, they decided that something had to be done.
The Professor, leader of the Annex Gang, organized a city-wide dragnet to track down the thieves. Before the adventure was over there was an exciting chase and a wild ride in store for Red, the Gang's War Leader.