Just Before Dawn.

Dr. Robert Ordway, the "Crime Doctor" is called on an emergency to a party at his next door neighbor, where a man, Walter Foster, suffers from a diabetic seizure and has collapsed on the floor. Robert administers insulin to the man, using the man's own case, but a short while after the injection the man dies. Robert's services is used to aid in the following investigation, and he gets a list of the guests at the party. He starts questioning them, one by one, beginning with the dead man's sister, Claire Foster. Claire calls Robert and asks him to come to her apartment