Spiral Staircase' Part 1

An ancient artefact, 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...