The fourth book in the famous Lewis Barnavelt series

Mrs Zimmermann is at a loss - she still hasn't regained her powers from her last encounter with dark magic and Uncle Jonathan and Lewis have left for the summer to travel around Europe, leaving her and Rose Rita bored and lonely at home. That is until Mrs Zimmermann keeps on seeing visions and shadows of her old magic teacher, Granny Wetherbee, who is trying to contact her from beyond the grave.

Mrs Zimmermann and Rose Rita set off to Pennsylvania to solve the mystery and in doing so travel back in time to Granny Wetherbee, who tells them that they must save a good wizard, Grandpa Drexel, who is destined to die for a wrongdoing he didn't commit.

As they both try to change the past, evil lurks in the background - Mrs Zimmermann is struck by amnesia and they must face a local wizard with a grudge and an old score to settle. Will Mrs Zimmermann regain her memory and her powers? Will they be able to right a past wrong? Will they make it back home alive?