Originally from the Warren of the Shining Wire, Flax left with Marigold and Hickory to live at Redstone. When Weedstalk and Chafe (actually Woundwort and Vervain) began to take over the warren, Flax was told he could not go visit a friend of his who was a squirrel, due to Weedstalk's disapproval of rabbits "consorting with non-rabbits."
Regardless, Flax, like the majority of the Redstone rabbits, regarded Weedstalk as the hero of the warren after he got food for them and even claimed to have run off a poacher. Thus, he did not object when Weedstalk was appointed Chief Rabbit, and mindlessly followed his and Chafe's orders.
Flax later provided much-needed emotional support to Hickory after the apparent death of Marigold, and even saved Hickory's life when he was buried in a cave-in caused by bulldozers come to destroy Redstone. Flax then left with Hickory and the others to live at Watership Down.