When a lothario is killed, Castle and Beckett suspect that the victim's mysterious double life holds the key to his murder.
The tenth anniversary of 9/11 proves a wrenching but clarifying passage for Mac, who suffered a terrible loss on that day. Meanwhile, an open-and-shut robbery/homicide proves more complicated than anyone had anticipated.
Trudy learns that efforts are being made to quash a burgeoning astronaut training program for women; John Glenn thinks about running for public office.
Deke and Marge embrace new roles to accommodate his new status; things start to thaw between Gordo and Trudy.
With the launch of the Gemini missions and the Apollo program's progress, pressure on the wives grows; Marilyn Lovell conceals a pregnancy.