The 5th Horseman by James Patterson

A young mother is recuperating in a top San Francisco hospital when suddenly she’s gasping for breath. The call button fails to bring help in time. How and why did this happen?

With help from the newest member of the Women’s Murder Club, Yuki Castellano, Lieutenant Lindsay Boxer discovers that this is not the hospital’s first suspicious case. Other patients have taken unexpected and devastating turns for the worse just as they’re planning to go home. Are these just appalling coincidences? Or is a maniac playing God with people’s lives?

When someone close begins to exhibit the same terrifying symptoms, Lindsay fears no one is safe. In a wild race against time she must fight an administration determined to shield its reputation even if it means hiding a killer…