Political Suicide by Michael Palmer

Lou Welcome is a doctor who works with other doctors with substance abuse problems. One night his friend, fellow physician Gary McHugh, is arrested for the murder of a politician after a night of heavy drinking. Lou can't believe his friend is guilty and immediately starts trying to prove his innocence.
Gary's lawyer, Sarah, doesn't want Lou to interfere but soon the two are working together--and stumble upon a powerful conspiracy while trying to find an alternate suspect. And their lives are in danger.

While the story seems a little far-fetched, it is engrossing. And you like both Lou and Sarah as well as Lou's precocious daughter, Emily. Great book for a day at the beach.