The Holmes Brigade — F.C. Shaw

In book 3 of the Sherlock Academy series, Sherlock Academy is out for Christmas break, but Rollie and Cecily are ready to solve their third mystery. When Rollie finds a letter in his great aunt's study questioning his decision to attend Sherlock Academy, he confronts her and finds out that his aunt can be just as determined and stubborn as he is about keeping secrets. Aunt Ei's secretive manners aren't the only mystery brewing: an agent from Scotland Yard and Wesley arrive at Rollie's house for protection, having just barely escaped from the clutches of Herr Zilch's henchmen. Even with the fun of friends and the holiday, Rollie still spies strange happenings at Herr Zilch's old mansion and goes with Cecily and Wesley to investigate. Between his grumpy aunt, protecting Wesley, and exploring Zilch's mansion, Rollie holiday turns out to be more than he expected.