Christ-mythers have a pretty big arsenal of arguments. They cite dozens of pagan parallels to Jesus, supposed New Testament silences, interpolations and contradictions. When combined they sound impressive, but they ultimately make for a better comedy routine than plausible history of Christianity. In the course of reading biblical scholarship that becomes clear. The truth, however, is that most people, whether believers or skeptics, have neither the time nor desire to take on such in depth study.
Most scholars and apologists will only go as far as looking at mythicists funny for even proposing that Jesus didn't exist, and rightly so. But realizing how well the internet can enable stupidity, Holding and his co-authors have collected every mythicist argument concocted in the last 150 years and thoroughly refuted it.
STCM is divided into roughly three sections, each dealing with different versions and aspects of the Christ-myth. The first puts the screws to the silence thesis as advanced by Earl Doherty; the second with the copycat thesis as argued by Acharya S and Robert Price; and the third addresses two "documentaries" about the Christ-myth and other miscellaneous arguments.
The most useful, although most mind numbing, portion of the book is the section dedicated to Earl Doherty's massive list of New Testament silences. Doherty's argument goes like this: If Jesus were a historical figure, he would have been mentioned by Paul where the latter discusses an issue Jesus also taught about in the Gospels. Since there's no mention of Jesus in these passages, he probably didn't exist. The argument takes on a few different forms, but that's the gist -- Christian author (take your pick) doesn't mention Jesus where he should have.
Holding et al. argue that the authors of the New Testament Epistles (NTE) usually didn't have a reason to recount the information about Jesus contained in the Gospels, because their audiences already knew it. As Holding puts it, "The entire silence mythicist thesis is premised upon a gross anachronism," that Paul, for instance, didn't know something about Jesus unless he specifically stated it in one of his letters.
Doherty has made a handful of attempts to address this criticism, in his 2009 book for example, but each falls short. When the people doing the original research think you're nuts, there's simply no place to turn for evidence in support of the argument. See my earlier point about scholars just giving mythicists the evil eye.
STCM also contains a very thorough defense of the extra-biblical references to Jesus. I found this especially entertaining because I read Holding's book shortly after reading Nailed, which was published almost two years later. Fitzgerald, however, doesn't appear to be aware (or ignores) that the arguments he uses against the partial authenticity of Josephus's discussion of Jesus, for example, were deflated long before his book was released.
I realize that these secular references are of limited value, and the argument for historicity ultimately has to go back to earlier sources. But the fact that writers like Tacitus and Josephus, whose competence is usually not doubted by scholars, mention Jesus and confirm some of the basic details of his life, is a point worth considering -- and defending.
The pagan copycat thesis, in all its forms, is also torn to shreds in the book. The parallels between Jesus and other religious figures from ancient world are generic, non-existent or the figure in question postdates Christianity, so the borrowing goes in the wrong direction.
But some mythicists take a more nuanced approach, suggesting that Christianity developed like many cults did in first century Rome. And as a result, the religion belongs in the "ancient savior god cults" category, as Doherty puts it. That's more likely. But as Holding rightly notes in response, putting Christianity into such a category doesn't necessitate any sort of copycat thesis and isn't "...relevant to whether or not it or any other tradition is 'divine truth.'" (p 275)
In summary, STCM is a comprehensive refutation of the Christ-myth, loaded with scholarship many readers otherwise wouldn't be exposed to. However vociferously mythicists may protest ("He's mean!" etc.). It's more a history book than a work of apologetics, and I think anybody interested in the historical Jesus question would find it useful.