This challenge will be slightly different than my others, as I will only put up the premise, and you can do whatever you wish with it.
When Voldemort first heard of the prophecy, the Longbottoms and the Potters had only defied him once, and they didn't even know they were expecting their children.
When they defied him again, and rumors began to circulate about the pregnancies of Alice Longbottom and Lily Potter, he became interested in testing their wills, by giving them one last chance to join him, to see which family fit into the prophecy.
Peter Pettigrew is aware of the plans made for his friends, and on an impulse asks James what would he do in order to protect his family, if the only choices were to join the Dark Lord, or fight until they were all dead.
Finally, when Voldemort asks the Potters if they will join his side, James Potter shocks everyone when he agrees, and takes the Dark Mark.
The entire thing, even what is written above, is up to you, provided that the general idea is intact. That is, James Potter decides that the survival of his family is more important than his pride or desire of glory.
This is, of course, a story that must have Snape and Harry interaction. The reasons behind this interaction are up to you, however, my restrictions are the same as my other challenges: Snape is not a child abuser, characters needing more than one dimension, etc.