The dark tide, by Andrew Gross

Karen's husband is killed in an explosion at Grand Central, a terrorist attack. A year later, watching footage of that awful day, she glimpses him -- after the explosion, hurrying away from the scene. Meanwhile, a detective is investigating hit-and-run accident that seems to be linked to Karen's dead husband; other people are looking for him too, claiming that they are owed hundreds of millions of dollars. Gross does a nice job of keeping you guessing.