Genius Tracey Houston

2005: Sabine Moriarty's estranged brother, Jim, uses the 7/7 attacks as an pretext to reconnect. She reluctantly agrees to meet him, hoping that in the years of their separation he has recanted his criminal ways and turned over a new leaf. He hasn't. He has a new project, and wants her help— to be the undoing of Sherlock Holmes.
In the 1970s, young Jim tries to send his sister to a magical land.

In the wake of the arsons, Sabine tries to derail Jim's attempt to frame Sherlock Holmes.
Back in the 1970s, young Jim shows Sabine what adults do.

Sherlock and John chase down the latest murders. Sabine tells her old math friend Aidan about a remarkable new theorem. After Jim lets Sabine see where he lives, he drops dark hints of a new plot. Sabine decides it's time to send Sherlock a new code.
In the 1970s, young Jim tries to save his family further trouble.

Sherlock takes on a case involving the apparent suicide of a celebrated interior designer, but the trail leads him back to Sabine, and Sabine back to him.
In the 1970s, Mr Moriarty decides to separate young Jim and Sabine by sending them away.

Realizing it's too dangerous to continue, Sabine delivers a dire warning- along with a hint about her past. John extracts an awkward confession, and the message in the mirror reappears.
In the 1980s, teenage Sabine and Jim reunite for a few stolen moments at a family funeral.

Sabine gives Sherlock her mobile number, forbidding him from calling her- leaving Sherlock to interpret the message.
In the early 1990s, young Sabine arrives at Oxford University, and is delighted to find her brother there- a changed man, and in love.