Agatha Christie 
Elephants Can Remember 

Hercule Poirot is determined to solve an old husband and wife double murder that is still an open verdict…Hercule Poirot stood on the cliff-top. Here, many years earlier, there had been a tragic accident. This was followed by the grisly discovery of two more bodies – a husband and wife – shot dead.But who had killed whom? Was it a suicide pact? A crime of passion? Or cold-blooded murder? Poirot delves back into the past and discovers that 'old sin leave long shadows’.