Meredith and Derek get one last shot at success in their clinical trial; the surgeons work together to free a boy from a block of cement; Izzie helps Alex care for Rebecca; Lexie uncovers critical information about George's status as an intern.
The team searches for a serial killer along the Appalachian Trail in rural Virginia.
Carter and Benton share a personal tragedy; bullets injure members of a bridal party; Charlie's mother appears; Jeanie and a doctor hit it off.
Archer, Reed and Major Hayes infiltrate a Xindi-Sloth plant that synthesizes vital explosive material for the Xindi superweapon.