In the novel They do it with Mirrors, John "Johnnie" Restarick was the second husband of Carrie Louise. When they married, he already had two sons, Alexis and Stephen. His first wife, the mother of his sons, was Russian.
After his divorce from Carrie Louise he married a Yugoslavian singer. The couple died in a car crash not long after that.
Among the adaptations, Johnnie Restarick is usually already deceased as in the book. Only in the ITV 2009 adaptation of the novel does he appear in person and takes on the role of Alexis Restarick who does not feature in the plot. Here he is divorced from Carrie Louise but keeps writing her long letters, hoping to come back, although she had already married Lewis Serrocold. He chatted up Juliet Bellever and convinced her to leave the lodge gate open for him. Using this, he arrived at the house just around the time of Guldbransen's murder. Johnnie is later killed when he is backstage at the theatre in the house and a rail of lights fails on him.
Miss Marple later surmised that this was because he knew too much or had suspected too much about how Gulbrandsen had been murdered. He had arrived at the house in the fog and had had heard a gunshot and then running footsteps outside the drawing room. He had commented that the drawing room appeared like a stage set. Lastly, he had asked for some nail clippings from Carrie Louise. Like Miss Marple in Murder with Mirrors, an earlier adaptation, these nail clippings would have shown that Carrie Louise wasn't being poisoned and that this was merely a misdirection.