Contagion is told like a murder mystery, but we care less about the strict ordering of events than about the people involved; the best substory has a romeo and juliet forbidden by fear of disease.

As the epidemic expands, Meme As Virus shows up with an internet scoundrel blogging about the epidemic and claiming that Forsythia cures it. In the end, millions die and he makes millions.

Plagues steal our friends and replace them with a quarantined Other. Smiles and greetings become false advertisements for the Death hidden within. There's more to mine in this topic; you gotta stop someplace, though. ;)

Update 2011-09-20
The question of the moment is:

Like normally healthy people get on the bus and before not too long, the bus is on fire and plummeting off a bridge. Searching for a vaccine, we discover that Aliens engineered it. Could have a very satisfying Luke-Skywalker-death-star flawed-hero-redemption scene as onslaught-of-the-unknown versus the loss-of-control of fire. the original technology.