Sherlock and you hadn’t been the most active with recent cases as of late since you two just had a baby, you were on maternity leave from having a c section done and Sherlock stayed home to help since John had advised him too (also sorta scared him into doing it by showing what stitches for c sections popping open looked like).

Now you were able to return to Scotland Yard to work leaving the baby with Sherlock, unfortunately Sherlock was called to a case by Lestrade so he had no choice but to put the chest baby carrier and take her since Mrs Hudson was on vacation

So here he was waving a rattle infront of the baby’s face as he looked over a dead body with Lestrade watching him