Their last time-travelling mishap still fresh in their minds, Grace and Jack are on edge about what might happen next. Grace's memories of her solo trip to the future are never far away. When the future begins to seep out into the present, they must stick to the rules or risk the consequences. They set themselves the task of finding out more about the mysterious ink, ending up in the past in a mysterious science lab. Could their new discovery also shed some light onto their mysterious friends at 21BUT22?