The novel opens in April, shortly after the death of the Lorimers' father. The house and most of their belongings are to be sold in the coming week, leaving the four Lorimer sisters – Fanny, Gertrude, Lucy, and Phyllis – very poor. The young women realize that they must find a way to earn money in order to support themselves. Gertrude, the novel's central character, proposes that they open a studio and put their skills in photography to use. They decide that Gerty, Lucy, and Phyllis will operate the studio while Fanny acts as housekeeper.
Lucy departs for a three-month apprenticeship at the successful photography studio of a family friend while Gerty begins to seek a location for their own studio. She leases two floors with an attached studio at 20B Upper Baker Street which they can afford with the modest means left to them. The sisters, with help from their friends the Devonshires, labor through all of June to prepare the studio for its opening. The studio opens at the end of July after Lucy returns from her apprenticeship. The Lorimers receive steady business from friends and acquaintances through the fall, though many customers hold a prejudice and expect to pay less for their services than they would for male photographers. Soon the Lorimers are hired to photograph artists' works. They begin making connections within the artistic community of London.
Post-mortem photography grew in popularity in the Victorian era.One evening in October, a housekeeper arrives at the studio and requests their services to photograph the recently deceased Lady Watergate. Though the prospect makes Gertrude uncomfortable, she accepts the job. While Gerty photographs Lady Watergate, the motionless silence of the gloomy Lord Watergate leaves a vivid impression in Gerty's mind.
Frank Jermyn, an artist who lives across from the Lorimers, visits the shop to hire the sisters to photograph his work. In need of income, Lucy accepts the job and enters Frank's studio unaccompanied despite the social impropriety of the action. Frank recommends the Lorimers to his artistic acquaintances. Soon the Lorimers' business grows, and Frank becomes a common visitor and good friend to the sisters.
The Lorimers are hired to photograph the work of Sidney Darrell, a member of the Royal Academy prominent in London society. When Gerty arrives at his studio, she is uncomfortable and detects a lurking contempt behind his polite indifference. She self-consciously photographs Darrell's work and is relieved when her job is over.
In March, Frank invites the sisters to attend a showing of his work. Many members of the artistic community attend the event, including Mr. Darrell and Lord Watergate. Despite her shabby mourning clothes, Phyllis's beauty catches the attention of both men. After the Lorimers leave, Lord Watergate asks Frank if they might make photographs for him to use during his scientific lectures at the Royal Institution. Soon, the sisters receive more work from Lord Watergate as well as Mr. Darrell. Darrell soon invites the sisters to attend a private viewing of his own work, where he asks Phyllis if she will pose as Cressida for him. Gertrude does not like the idea but cannot stop the sessions from beginning. Under Fanny's supervision, Phyllis soon begins to sit regularly for Mr. Darrell. He gives her frequent gifts, and Phyllis enjoys Darrell's attention.
One evening in June, Frank Jermyn arrives at the Lorimers' unexpectedly. He tells the sisters that he is to leave for Africa the next day as a special reporter to make newspaper illustrations. Frank proposes to Lucy. They have each been fostering growing feelings for one another and Lucy joyfully accepts. Frank leaves for Africa the next morning.
Rumors surrounding Phyllis' modeling spread throughout the summer. Gerty is worried that Phyllis cares too much for Darrell. When Mr. Darrell announces that he must leave for Paris and cannot finish Phyllis' portrait, Phyllis is hurt by his unexpected departure.
In September, the girls learn of an ambush of British troops in Africa that leaves nearly all killed. However, Frank Jermyn is among those who are missing. Lucy soon departs to visit Frank's parents at their request in Cornwall in order to grieve together. Gertrude sees Lucy to the station. When she arrives back at the studio, she finds Lord Watergate there to discuss business. However, they find a note which Phyllis has left to say that she is running away to Italy with Mr. Darrell. Gerty and Lord Watergate are alarmed; Lord Watergate informs Gerty that Mr. Darrell is already married. The two rush off to Mr. Darrell's together but fear they will be too late to stop the pair. Gertrude and Watergate have arrived just in time. Gertrude storms into Darrell's studio and convinces Phyllis to return home over the protests of Mr. Darrell. Lord Watergate denounces Darrell as a scoundrel. Phyllis faints, and Gerty and Lord Watergate rush home with her. Phyllis is very unwell after this. She has consumption, and a physician tells Gerty that Phyllis' death within months is certain. Phyllis dies within a few weeks.
Lord Watergate pays Gertrude a visit a few weeks later with the news that there is a rumor that Frank has been seen alive. An emergency expedition finds Frank. By March, he has returned to London. Lucy and Frank are to be married immediately. Lucy will carry on the photography business after marriage. Gertrude's own future is uncertain, and she turns away Lord Watergate's advances in a tearful burst of emotion.
Weeks later, Frank and Lucy are married and away on honeymoon, and Gerty is left alone in the studio. She painfully reflects on her uncertain future and playing out the part of a "strong-minded woman" into which she had been cast. She regrets that she turned down a future of love when she sent Lord Watergate away. However, there is suddenly a knock at the door; Lord Watergate has returned in spite of Gerty's rejection. Gerty tells Lord Watergate that she did not reject him because she did not value his love, but because she was afraid of embracing the happiness he offered.
The novel's epilogue details the sisters' lives after marriage. Fanny and her husband remain happy together, but wish for children. Lucy and Frank have two children, but Lucy continues photography and specializes in children's portraits. The Watergates also have a child, and Gerty hopes he will inherit Lord Watergate's scientific mind.
