** spoiler alert ** 
 This was definitely much better than the third book. The story was more believable (though like Brown's other books, it's definitely out there) as there is no conspiracy theory type plot. The plot is definitely more grounded in terms of fact (though Brown does make a mistake in terms of researching. He makes a reference to a Kentucky Derby winner and the name of the farm of said winner. However, the horse he name was disqualified and is not considered the winner of the Derby and he mis-spells the name of the farm!). I would rate this 3.5 but the ending... was just a drop out... there wasn't any resolution. Its as if they realize they virus is already out there and they go on about their daily lives like nothing every happened. It was a little disappointing and a little let down