Samantha Morton’s affinity for playing complex, richly layered mothers—an 18th century brothel madam in Harlots, the leader of a group of post-zombie apocalypse survivors in The Walking Dead—is a genre-crossing body of work for the actor’s actor, and a rich, years-long gift to TV fans. Morton’s latest entry in this category of formidable schemers and strategists is Catherine de’Medici, the Florentine orphan who became Queen of France in 1547, in Starz’s historical costume drama, The Serpent Queen.