Osborne, Mary Pope, Magic Treehouse #46, Dogs in the Dead of Night
The fan-favorite chapter-book series whisks Jack and Annie back in time to the Swiss Alps in search of a rare flower. When they find a monastery where monks and St. Bernards live, Annie offers to train a young dog named Barry. Then Barry runs away, and Jack and Annie have a new task to find Barry! Will he lead them to the mysterious flower? Or into danger?