Lily became pregnant in the autumn of 1979 and the Potters went into hiding. On 31 July, 1980, Lily gave birth to their son Harry James Potter, but it wasn't long before Albus Dumbledore found out that they were in grave danger. Young Harry had become a target of Lord Voldemort, because of a prophecy concerning the one who could ultimately defeat him for good.^[11] Voldemort had learned of the prophecy through his follower, an old enemy of James and the former best friend of Lily, Severus Snape.
When Snape learned about Voldemort's decision he pleaded that his
master spare Lily, thereby putting James and Harry's lives at stake.

In 1981, Dumbledore told the Potters that their best chance of remaining safe against Voldemort was the Fidelius Charm. James insisted on using Sirius as their Secret-Keeper, even though Dumbledore himself had offered to fill the position.^[9]
Sirius however, had a different plan. He convinced James and Lily to
use Peter as their Secret-Keeper, with Sirius as a decoy. They agreed
and Dumbledore cast the charm in secret, but this attempt at a
double-bluff ended in tragedy. The only people to know about the switch
were James, Lily, Sirius, and Peter. Even Albus and Remus were kept in
the dark. Less than a week later, Peter betrayed the Potters to Voldemort.^[9]