Last year’s Victorian-themed Christmas special may have divided viewers, but fans will agree that tonight’s thrilling comeback signals a spectacular return to form. Baby Watson is born, and Sherlock must negotiate the delicious prospect of having someone more childish than him around.

Meanwhile, the proud sociopath is haunted by the spectre of Moriarty, convinced that every case leads back to his nemesis. Amid a flurry of crimes to solve, one stands out: a mysterious death leads him to discover a bust of Margaret Thatcher, stolen and smashed by a stranger.

What’s Maggie got to do with Moriarty? And what’s going on in that mind palace of Sherlock’s? A globe-trotting, surprising, sucker-punch of an episode that will have you counting down the days until the next instalment…