Dr Sanders, a forensic working on a poisoning case is walking back to his home after a long day at the office. In the middle of the night he is asked for help by a beautiful young woman who asks him to accompany her to a a certain Mr Felix Haye's flat. On reaching there he is shocked too find a gathering of 4 people who look like dummies, all of them have been heavily drugged and Mr. Haye is found murdered.
The Police find that the guests were poisoned by someone who rigged their drinks by putting atropine in their glasses. So what's so Carr(read impossible) about this murder? Once the remaining guests are revived, their statements corroborate that no one poisoned the drinks and that the glasses were watched all the time.
Add in the conspicuous disappearance of a prime suspect, another murder and a truck load of suspects and we have a case for the Old man.