All law is based on human evidence and since human beings are what they are, their evidence cannot be infallible. Is it therefore justifiable to take the life of one man on the evidence of another? This is the argument on which "Kanoon" is based and it is told with the help of five characters. Or may be six if you count the dead man. Judge Badri Prasad (Ashok Kumar) is seen committing a murder by his son in law to-be Kailash (Rajendra Kumar). However an innocent petty thief is arrested for the crime just because he happens to be at the wrong place at the wrong time. The trial is in the court of Judge Badri Prasad. Kailash, the public prosecutor is dumb founded to see an innocent man being accused of a crime, which he had not committed. Kailash decides to defend this innocent man. Kailash is faced with the dilemma of knowing who the real murderer is, but cannot expose him. At the same time he must save the life of the petty thief that has been wrongly arrested for a murder he has not committed.