Complex sentence: Emerson played Ben Linus on television's "Lost", and Preston was a guest star in episode 20 of season 3, "The Man Behind the Curtain" as Ben's mother Emily in flashback scenes, though she and Emerson never shared scenes together.
Split into simpler sentences: Emerson played Ben Linus on television's "Lost", and Preston was a guest star in episode 20 of season 3, "The Man Behind the Curtain". She played Ben's mother Emily for several flashback scenes, though she and Emerson never appeared in any scenes together.