This unusual biography traces the life of Flush from his carefree existence in the country, to his adoption by Ms. Browning and his travails in London, leading up to his final days in a bucolic Italy. The story begins by alluding to Flush's pedigree and birth in the household of Barrett Browning's impecunious friend Mary Russell Mitford. Woolf emphasises the dog's conformity to the guidelines of The Kennel Club, using those guidelines as a symbol of class difference that recurs throughout the work. Declining an offer from the brother of Edward Bouverie Pusey for the puppy, Mitford gave Flush to Elizabeth, then convalescent in a back room of the family house on Wimpole Street in London.

Flush leads a restrained but happy life with the poet until she meets Robert Browning; the introduction of love into Barrett Browning's life improves her health tremendously, but leaves the forgotten dog heartbroken. Woolf draws on passages from the letters to depict Flush's attempted mutinies: that is, he attempts to bite Browning, who remains unharmed.

The drama of the courtship is interrupted by Flush's dognapping. While accompanying Barrett Browning shopping, he is snatched by a thief and taken to the nearby rookery St Giles. This episode, a conflation of three real times on which Flush was stolen, ends when the poet, over her family's objections, pays the robbers six guineas (£6.30) to have the dog returned. It provides Woolf the opportunity for an extended meditation on the poverty of mid-century London, and on the blinkered indifference of many of the city's wealthy residents