Life becomes too rough in the mountains -prey is scarce and it's cold. Stoneteller receives a dream from the Tribe of Endless Hunting (the Tribe of Rushing Water's ancestors) showing her the Sun Trail.
The Tribe decides to take a vote. More cats want to leave, so the cats who voted to leave set out along the Sun Trail while the rest stayed. Gray Wing doesn't want to leave, though his two brothers do.
Jagged Peak, Gray Wing's younger brother, wants to leave. After the cats left, he went missing. The cats assumed he went after them, which he did. Gray Wing set out on the Sun Trail to find his younger brother.
Once he found Jagged Peak, they were too far to turn back to the mountains so they continue along the Sun Trail until they encounter the others. They then join them on their journey to their new home.
On the journey, they encounter an eagle who tries to catch them so it can eat them. They make a plan, however Gray Wing is caught by the eagle so Bright Stream saves him. In the process, she is taken and carried off by the eagle instead. Afterwards, Clear Sky, Gray Wing's littermate (brother) reveals that Bright Stream had been expecting his kits.
Once they arrived, they separated so one group went to live on the moors under Tall Shadow's leadership while the others went to live in the forest under Clear Sky's leadership. Gray Wing falls in love with a loner but it turns out she's Clear Sky's new mate. Later, she dies protecting her three kits from a monster (human vehicle). However, only one kit survives. He is rejected by his father so Gray Wing takes him as his son and names him Thunder.