It means there is nothing there that should keep author and reader from moving on with the story. Since as the following sentence explains, Who he was, where he came from, and what he did are of no great importance.
Having a look at need detain, it's pretty straight forward.
As for Quinn, there is little that need detain us. It can be rephrased as, there are not many reasons that make it necessary to be detained at that place in the story.
The dictionary shows us
detain: Keep (someone) from proceeding by holding them back or making claims on their attention -ODO
need: [AS MODAL, WITH NEGATIVE OR IN QUESTIONS] Expressing necessity or obligation: -ODO