1. Boom
Proving once again how masterful he is at one-off episodes, Steven Moffat is behind the best episode of the season: "Boom." The concept is simple: The Doctor stepped on a landmine and cannot move without his own body becoming an explosive. But as he looked for a way out of the predicament, he and Ruby had to deal with matters of family, war, and capitalism.
The minimalist setting and plot forced the actors to work ten times harder to keep the audience's attention, and they pulled it off. The episode is rife with tension, and Ncuti Gatwa gets some of his most effective Doctor moments yet. His chemistry with Milly Gibson is excellent, and the themes of the episode translate well.
Adding to how effective it is as a one-off, "Boom" does a good job bringing the Susan Twist appearances to the surface and features upcoming companion actress Varada Sethu in a similar vein to Jenna Coleman's appearances before her formal run as Clara Oswald. There's a lot to love in this episode, which will surely be remembered as a stand-out for the show moving forward.