After the disastrous Christmas party, Lady Constance decides to take the whole family away from repairs at Ashton Place to London for awhile. Penelope is thrilled but quickly lost as the guide given to her by her old headmistress turns out to be no help at all. Simon, a young playwright, comes to her aid. The children have many adventures and Penelope uncovers more strange and enigmatic clues about the children - and makes a startling deduction about Lord Ashton!