When Mycroft mentioned "the other one," he was referring to Enola Holmes, his and Sherlock's much younger sister. The free-spirited black sheep of the family was not only incredibly smart and independent, but also a very accomplished hacker. However, her hacking got her into trouble with the government. Mycroft made it so she could avoid jail time, but the catch was that Enola had to attend a reform boarding school (much to her horror).
She comes home for the holiday and discovers that only has her brother, Sherlock (whose she's always connected to more), was not only shot but now he's being sent off on a suicide mission for killing a bastard who deserved it? Not on her watch.
So being the extraordinary tech-geek she is, Enola creates the Moriarty GIF and scatters it across England, thus saving Sherlock.
Bonus: John being annoyed about Sherlock never telling him about his sister but then endeared by how much Sherlock adores her. Double Bonus: Mycroft and Enola putting aside their differences and bonding over a shared protectiveness of their sibling. Triple Bonus: Enola visiting 221B Baker Street and helping solve a case.
The Other One - Enola Holmes, BAMF Little Sister
She comes home for the holiday and discovers that only has her brother, Sherlock (whose she's always connected to more), was not only shot but now he's being sent off on a suicide mission for killing a bastard who deserved it? Not on her watch.
So being the extraordinary tech-geek she is, Enola creates the Moriarty GIF and scatters it across England, thus saving Sherlock.
Bonus: John being annoyed about Sherlock never telling him about his sister but then endeared by how much Sherlock adores her.
Double Bonus: Mycroft and Enola putting aside their differences and bonding over a shared protectiveness of their sibling.
Triple Bonus: Enola visiting 221B Baker Street and helping solve a case.