This is the disturbing story of Dr. Jan Karbaat, a fertility doctor who used his own sperm to get his patients pregnant without them knowing it was his.

Recently, there have been increasing reports of fertility doctors who used their own sperm on their patients in the 1970s and 1980s. Dr. Karbaat was the first doctor whose shocking practices came out.

As a result, Jan Karbaat's descendants were forced to come to terms with the true identity of their biological father and the realization that their existence had begun with deceit. In addition, all of a sudden they were faced with the fact that they had dozens of half-brothers and sisters at once, and new 'children of Karbaat' are discovered every year.

In Investigators, we hear the stories behind some of the world's most intriguing investigations, told through the eyes of those who conducted them.