Graystripe's Vow (Warriors Super Edition, Bk. 13)

Shadows have lengthened on the time of the Warrior Clans. . . .

Graystripe served ThunderClan for many moons before retiring to the elders' den. He was Firestar's best and most trusted friend, relied on to ensure the clan's safety during times of great turmoil. And as new tensions and doubts strain ThunderClan nearly to breaking, Graystripe will need to call on all of that long history - and leave ThunderClan behind in hope of finding an answer that might save it.