“Isn’t she just ‘it’?” a partygoer observes of Lady Eileen Brent (Mia McKenna-Bruce), blessed with the rather adorable nickname of “Bundle” and daughter to Lady Caterham (Helena Bonham Carter), British gentry fallen on hard times in the aftermath of World War I. Bundle is, indeed, “it,” a description lifted directly from the two Agatha Christie novels (The Secret of Chimneys and The Seven Dials Mystery) featuring this plucky, mystery-solving heroine, who gets to be front and center in Netflix‘s new three-part drama, Agatha Christie’s Seven Dials. Agatha Christie’s Seven Dials The Bottom Line Superb lead turn covers for laggy patches. Airdate: Thursday, January 15 (Netflix)Cast: Mia McKenna-Bruce, Helena Bonham Carter, Martin Freeman, Edward BluemelCreator: Chris Chibnall In order for Seven Dials to work, McKenna-Bruce must also be “it”; the series hinges not just on viewers marveling at her gumption, shrewdness and other synonyms for “pluck,” but on viewers wanting to watch Bundle’s further adventures, which are surely set up by Chris Chibnall’s (Doctor Who) adaptation. Fortunately, McKenna-Bruce is absolutely “it.” The 28-year-old actress brings ample …