When Lake Nasser threatened to flood the complex in the 1970s, engineers had the unenviable task of formulating a plan to save it and this they did with consummate skill.
The flood injured and killed lots of people. 
mnli hypothesis: The flood injured and killed lots of people.  premise: When Lake Nasser threatened to flood the complex in the 1970s, engineers had the unenviable task of formulating a plan to save it and this they did with consummate skill.