Possible Clues:

• Disinterested in right and wrong
• Scent sent back by student without scruples?
• Unacquainted with ethics
• Like the stranger in Camus's 'The Stranger'
• It's quite wrong that this could be a lesson on how to be quite right
• There's a lesson to be learned from being so bad
• That's no good by the end of the morning, in a manner of speaking
• Having no sense of what is right
• With no concern for right or wrong, Miss Marple's all but last following up scent
• For the unprincipled, there's a lesson there