The arrival of a mysterious comet heralds impending danger from enemies both old and new. As Ace helps the Doctor defend Earth, she is confronted with a dangerous question..."Doctor Who?"

Hugo is a brilliant turn-of-the-century scientist, loved and respected by his family and friends, admired by his colleagues. But he is a man quickly becoming obsessed with a curious and frightening question... what is the mysterious apparition found in the photographs of his dying subjects?