Young Miss Holmes Casebook 1-2 by Kaoru Shintani
Pretend for a moment that Sherlock Holmes has a 10 year old niece as obsessed with puzzles as he is and just as smart. That's what you get in Young Miss Holmes. Young Miss Holmes, Lady Christie Hope, tackles several of Sherlock Holmes lesser known cases such as The Red Headed League and the Dancing Men, where she uses her own brand of sleuthing to solve the cases with her uncle.
This manga reminds me a lot of Case Closed by Gosho Aoyama. It's funny, and you have a pint sized detective who has to constantly prove their smarts to adults. Christie has a large dog named Nelson that she can saddle and ride like a dog. Her two maids are constantly trying to make her act more appropriately, but one carries two guns, and the other a whip to protect their mistress. I spent the entire comic dying to know their back story. At times Christie can be childish and she keeps bucking against being the type of nice young lady that society wants her to be. But she is as smart as Sherlock Holmes and at times actually figures out the case before him. She also drives everyone around her nuts. Christie is constantly sneaking out or manipulating people so that she can investigate whatever mystery comes her way. Her shenanigans often lead her into danger or back her into a corner. She thinks nothing of putting her life on the line to get to the bottom of the case, adding an element of danger to the comedy. It's no wonder her maids are well armed at all times. They never know when they will need to go running after Christie to save her life.
Those looking for a straight forward serious manga version of Sherlock Holmes will be disappointed, but if you want a fun new take on the Sherlock Holmes' adventures checkout Young Miss Holmes.