'Spiral Staircase,' Part 1. An ancient artifact, fused to the body of a movie star! An above-top-secret counter-UNIT organisation! A humungous jet-black tetrahedron from the heart of the Milky Way, hovering above New York City! The Doctor lost for words - and for answers! And amid the chaos, two friends, Gabby and Cindy, trying to work out if Gabby's adventures have left her forever changed!