When we last saw Grant and Lucy, they were settling down together with Lucy's daughter, and Grant's superheroic costume was being stored away. But that wasn't the end of the story! Soon, the Doctor is swooping back into their lives - because it turns out the alien gemstone that gifted Grant his powers of flight, super-strength, and super-speed has siblings all over the universe. It's up to the Doctor, Grant, Lucy, and their daughter to track them down to prevent disaster - from a post-apocalyptic New York, to a world taken over by the forces of the Harmony Shoal, to a boneship in the depths of space... and more!