Grave Passion

Two young lovers out for a night of romance. A short cut through a cemetery. They witness a murder, but there has been no struggle, only a knife to the heart.

It has all the hallmarks of an assassination, but who is the woman?

And why was she alongside a grave at night? And did she know the person who killed her?

And then, there are other deaths, seemingly unconnected, but tied to the family of one of the young lovers.

It's a case for Chief Detective Inspector Cook and his team, and they're baffled on this one.