This is the first time I've come across such a phrase (in a novel) and I couldn't find an explanation through an internet search.
Let's consider the following situation that Alice and Bob play Japanese chess. Alice expected what Bob do next, but Bob's next move was beyond her expectations.Then, maybe Alice said そうくるんですか to Bob.
そうくるか/そうくるんですか/そうきたか are used when something unexpected happened to narrator. Also, そうこなくっちゃ means that’s what I wanted to hear.
In this case a direct parallel English expression comes to mind:
"So it has come to that"
But as other users have pointed out, you should provide better context or no one will be able to give you a satisfying answer.