His first novel, the 2014 sci-fi thriller Koko Takes a Holiday, was the first in a series about the ex-mercenary Koko Martstellar, and was followed by a sequel, Koko the Mighty, in 2015. Publishers Weekly's review of Koko Takes a Holiday appreciated the "vigorous anarchic pulse" of Shea's narration, but considered that the story and setting, with its "many borrowed elements", held no surprises.[2] The Library Journal's mention of the sequel noted its "well-developed characters and nonstop action".[3]