“All rivers flow to the sea; yet the sea is not full.”

On the Thai island of Samui, widowed private investigator David Braddock is stuck in a rut. Spending his days pandering to disreputable clients and his nights engaged in meaningless sex, this is not the life he had envisaged for himself. It passes the time, but it is hardly exciting.

Professional assassin Ross Gallagher has the opposite problem. He is sick of excitement. Years of travelling the world murdering strangers has taken a toll on his mental health, and he wants a different kind of existence before it is too late.

But their fortunes take an unexpected turn – and not for the better – when Braddock receives a phone call from his daughter saying she has killed her husband …