The last few seasons have seen Doctor Who expanding its internal lore once again. “Lux,” the latest episode, continues that trend. With Ncuti Gatwa delivering another excellent performance, and Alan Cumming guest-starring as a murderous cartoon character, “Lux” takes some massive swings that are sure to be met with some controversy. However, Russell T. Davies pulls off one of his more enjoyable teleplays, acknowledging the greater Who-Verse in the process.

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In a Miami movie theater, the audience watches a newsreel highlighting the atom bomb tests out west. The projectionist readies a cup of tea while he prepares a new reel for the theater. The projectionist kicks off a cartoon titled “Ring-a-Ding,” featuring a blue cartoon man who sings and dances. The audience seems to enjoy it, when suddenly the light...