Tough, ambitious and hardworking, Natalie Reyes finds herself suspended - unjustly - from Harvard Medical School, and it feels like her world has ended.

But when her mentor sends her to present a medical paper at a conference in Rio de Janiero, it almost does...Kidnapped, and shot while trying to escape, Natalie is left for dead in an alley. Against all the odds she survives, but her dreams are shattered.

On the other side of the world, medical genius Joe Anson is working on a serum which could save millions of lives - if only he can fend off a fatal illness long enough to complete his research. But Anson is running out of time, and those watching from the shadows will stop at nothing to ensure he fails.

Meanwhile, in Chicago, disillusioned private detective Ben Callahan is struggling to identify a dead man; struggling to find an explanation for the mysterious marks on his body. But the answer could lead Ben into a conspiracy far wider than this case...

Three people with no apparent connection learn the meaning of trust and betrayal as they are drawn into the web of secrecy which surrounds the fifth vial.