Ellery Queen

The Adventure of the Eccentric Engineer (1x14)

: 18, 1976

Heeeeeeeeeeere's Ed. Ed McMahon, that is, who plays a once brilliant but now seemingly senile inventor who is murdered in his electric train workshop. This one's a toughie because it appears as though no one could have entered or left the workshop during the time in which the murder must have taken place.