Dead ringers

Doppelganger, previously unknown identical twin, clone? All these are questions that must go through Tess' mind when she swears she sees her ex-husband on the street. He looks EXACTLY like her ex-husband but it isn't him. Then she finds out that her best friend has been told she has an exact duplicate too. What is going on?

I'll not spoil anything by telling you, but I will say Christopher Golden writes creepy horror really well. This one doesn't disappoint.