Anna Katharine Green was an American poet and novelist. She was one of the first writers of detective fiction in America and distinguished herself by writing well plotted, legally accurate stories. Green has been called ''the mother of the detective novel.'' Ebenezer Gryce is thinking about quitting detective work, but a curious case delays his retirement. It's the murder of a wealthy old man in a locked room, a circular study with lights that change colours and walls that move. There's a also a talking parrot who keeps saying ''Remember Evelyn,'' and a servant who doesn't talk at all but is clearly a bubble off. What can it all mean? A clue leads Gryce to Miss Butterworth, who is only too willing to help the investigation.