Dr. Mann is finally able to isolate the source of Yorick and Ampersand's immunity. Unfortunately, that source is withing Ampersand's body, which was last seen disappearing under the arm of a mysterious Japanese mercenary. Now, accompanied by 355 and Dr. Mann, the last man on Earth has embarked on a new and even more hazardous journey -- following Ampersand's trail across the Pacific, where danger threatens from below as well as above the waves.