Sherlock and Redbeard

When Mycroft and Sherlock had gotten home from school to find their parents waiting for them by the front door with the Irish Setter, Sherlock had let out a cry of delight and rushed forward to the dog, who responded enthusiastically. Mummy had beamed, and Daddy had chuckled. Mycroft simply scowled. (Oneshot. Spoilers for HLV.)