Dr Penrose

In the novel Sleeping Murder Dr Penrose is a psychiatrist working at Saltmarsh House, a nursing home in Norfolk where Major Halliday spent the last years of his life. Gwenda Reed came to see him to seek information about Halliday who was her father.

Penrose told Gwenda that her father had an obsession or delusion that he had strangled his wife Helen Halliday, although he could not remember the act of actually killing her. Nonetheless the obsession was strong and he would not be shaken. He also believed that his wife had been administering  drugs to  him--thinking it was like the wives in India who drove their husbands insane with datura poisoning. He had apparently  suffered   often  from hallucinations,  with  confusion  of  time  and  place. This obsession was so strong that eventually he committed suicide.

Nonetheless, Penrose was certain Halliday could not have killed Helen. Halliday was most not  a  paranoiac  type. He had no  delusions  of  persecution,  no  impulses  of  violence. He was  a gentle,  kindly,  and  well-controlled  individual.

Penrose also handed over to Gwenda a diary which her father had kept while in the sanatorium.

There is very little description of Penrose in the text except that Gwenda Reed observed that Penrose "looked a  little  mad himself.  He  looked,  for  instance,  much  madder  than  the  nice  old  lady  in the  drawing-room" but perhaps it was because in Gwenda's view "psychiatrists  always looked  a  little mad".

BBC's Miss Marple
In the BBC 1987 adaptation of the novel, Dr Penrose is portrayed by John Ringham.