Just a few years back, we had a very different Doctor Who on TV.
In 2013, Peter Capaldi stepped into the role and went on to play a perturbed Time Lord who was only a white lab jacket away from being a live-action Rick Sanchez. Eventually, that unrelenting moodiness subsided to a more fun-loving version of himself, (hence the sunglasses and electric guitars) but he was still one of the edgiest and most substantial incarnations in the show's history.
Across the whole breadth of his tenure, whether he was nasty or nice, Capaldi gave it his all. There were good eps and less good eps, but he always manged to play the part full pelt. It allowed for a strand of highly memorable two-parters, and even the odd three-parter, but it also meant that the stand alone episodes were, by large, equally brilliant.
Furthermore, it could be said that the power of the stand alone ep was never stronger than during the Capaldi saga. So it's only fitting that we retrospectively celebrate some of the best ones. If you slept on these, then now's the time to hunt them down and catch up.