What Puzzles Me is How They Can Charge $750 Fora Drug Whose Patent Has Expired.

From the NY Times:
Specialists in infectious disease are protesting a gigantic overnight increase in the price of a 62-year-old drug that is the standard of care for treating a life-threatening parasitic infection.
The drug, called Daraprim, was acquired in August by Turing Pharmaceuticals, a start-up run by a former hedge fund manager. Turing immediately raised the price to $750 a tablet from $13.50, bringing the annual cost of treatment for some patients to hundreds of thousands of dollars…
Turing’s price increase is not an isolated example. While most of the attention on pharmaceutical prices has been on new drugs for diseases like cancer, hepatitis C and high cholesterol, there is also growing concern about huge price increases on older drugs, some of them generic, that have long been mainstays of treatment.
I accept that the trademark 'Daraprim' is protected, but surely the patent expired decades ago, so surely everybody else can happily manufacture generic versions and sell them for cost-plus?