2 1/2 stars
Decent debut novel in that it kept me turning pages and had a pleasant enough prose style. I also note that Cullen writes solidly in American English, with only the occasional "housing estate" getting past. The subtitle suggests that this will be the first of multiple Cody Stockton mysteries. Cullen's YouTube fanbase will likely buy them.
Alas...
The potentially interesting SF backdrop to the story—the AI war—serves as little more than a plot device, a touchstone for the protagonist's "war flashbacks," and the only explanation provided for why the story is set in 2045.
AI is the other SF element, serving as the "machina" in the title. A world that survived a war with AI in which a billion human beings died is deciding, after a mere decade has passed, to turn AI back on in the hope it will solve all of humanity's ills. (Sounds like humanity deserves what it gets.) Again, the storytelling possibilities around AI are myriad, and yet here they are all delivered via television announcements that characters overhear.
As noted, that was the "machina" in the title. The "deus" refers to Jesus and to his reappearance on Earth in 2045. Cullen's handling of the Second Coming was, frankly, preposterous.
I'm sympathetic to the overall thrust of the story here, that humanity needs spiritual, rather than technological, solutions to the many dilemmas it faces. I also appreciate the effort that goes into a debut novel. I have read much worse, and I enjoyed this as a light read.