Bigwig had entered Efrafa as a secret enemy, joining the Owsla and executing a daring escape with Blackavar and the does that ended in Woundwort's defeat as the Watership rabbits floated down the River Test in a punt (an idea that came from Blackberry and Fiver).
On the journey to Watership Down, Hazel's party were intercepted and challenged by an Efrafan patrol led by Captain Campion, who backed down upon seeing the large size of Hazel's party but followed them to Watership Down at a distance and then reported back to Woundwort, who immediately organised a war party.
The Efrafan war party was spotted by a mouse who had been saved by Hazel sometime before. The mouse told Hazel of the incoming enemy. Hazel bravely went alone to try and drive a bargain with Woundwort, suggesting that the Watership rabbits and Efrafans work together rather than fight, and that they could build a warren halfway between them to relieve the overcrowding in Efrafa. His offer was refused and countered with the demands that Bigwig, Blackavar, and the escaped does would be handed over immediately. Otherwise, Woundwort threatened, he would tear the throat out of every buck in the warren.
The Watership rabbits filled in all the entrances to the warren, so the Efrafans had to dig to reach them. The battle lasted all night as Woundwort and Bigwig fought inside the warren while Hazel, Blackberry, and Dandelion ran off with a plan to release Bob, the guard dog of Nuthanger Farm, and lead him to the Efrafans.
Bigwig guarded a run leading to a burrow in which the members of the Watership Down warren were sheltering (save Fiver, who was in a death-like trance and had to be left in the Honeycomb), including Clover and her litter and a pregnant Hyzenthlay. Burying himself under the floor, Bigwig hid until Woundwort broke in, attacking him from underneath and biting deep into the General's foreleg, injuring it so badly that Woundwort had to hobble on three legs.
Despite this crippling blow, Woundwort put up a ferocious fight against Bigwig, but ultimately succumbed to exhaustion and attempted to coax him out with false promises. Bigwig refused, loyally stating that his Chief Rabbit told him to defend the run and he would do so until told otherwise. No one had guessed that Bigwig was not the Chief, and this gave all the attackers pause, for they suspected that the mysterious Chief Rabbit would be even larger and stronger than Bigwig.
The General, wounded and exhausted, retreated and told Vervain to finish Bigwig off. Fiver, who had just awoken from his stupor, met Vervain in the burrow and prophesied his (Vervain's) death, scaring the latter back out into the open.
The dog finally reached the warren and attacked the Efrafans outside, killing a few and chasing off the rest. However, Woundwort fearlessly stood his ground. The fate of Woundwort himself is not exactly clear, as his body is never found, but he is never seen or heard from again by any rabbit, bird, or mouse near the down. Given that he was severely wounded and exhausted from his fight with Bigwig, it is highly unlikely that he survived.
As a result of this battle and his skill in returning to Efrafa with the patrol, Campion became the new Chief Rabbit of Efrafa, and Groundsel left to become the Chief Rabbit of a new warren called Vleflain, the very warren Hazel had proposed creating to Woundwort. Thus ended the conflict between Efrafa and Watership Down.