The family of James Sanderson are shocked when the doctor refuses to
sign his death certificate. The doctor suspects that he was poisoned.
Everyone in the household falls under suspicion - including the two
step-daughters Nina and Kate. Nina eats one of James' chocolates and is
ill afterwards - that was the way the poison was administered. So it
looks as if Kate is the murderer and when she later commits suicide it
can only be because she was guilty.