The story of Trust is told through four different documents. The first document is a novel-within-the-novel called Bonds by the author Harold Vanner. In Bonds, Benjamin Rask comes from the prominent Rask family. His ancestors started in the tobacco business. Both of Benjamin’s parents die while Benjamin is in high school, and he becomes the owner of the family company. He’s not interested in tobacco, so he sells his stake in that business and focuses instead on finances and investments.
Helen comes from the Brevoort family, a previously prominent family in Albany that has fallen on hard times. As a child, Helen moves with her mother, Catherine, and father, Leopold, to Europe. Her father educates Helen himself, but he becomes increasingly devoted to teachings that Helen views as nonsensical, like alchemy and necromancy. He suffers a mental breakdown and receives treatment in a Swiss sanatorium. Catherine and Helen ultimately return to New York, where Helen meets Benjamin.
When Helen and Benjamin first meet, Benjamin is a successful financier. Catherine puts a plan in motion to have Helen marry Benjamin, which will return the Brevoort family to its former renown. Benjamin is immediately taken with Helen. While Helen isn’t excited about the idea of the marriage, she feels like Benjamin might be a good match because they’re both relatively solitary.
After they marry, Benjamin and Helen find that they’re well-suited to each other and begin to enjoy having small concerts in their house. Helen becomes increasingly involved in philanthropy, and Benjamin enjoys even more success as a financier. He even makes a fortune from the financial crash of 1929, which decimates almost everyone else. That leads people to speculate that Benjamin’s investments might have in some way caused the crash.
Helen becomes afflicted with a mental illness that’s reminiscent of her father’s and insists on being treated in the same Swiss sanatorium where her father was treated. Benjamin bullies and coerces the head of the sanatorium, Dr. Frahm, into devoting an entire wing to Helen’s care. Benjamin gradually becomes dissatisfied with the care Dr. Frahm provides, even though Helen seems to be improving. He replaces Dr. Frahm with a doctor from a pharmaceutical company in which Benjamin owns a large stake. That doctor, Dr. Aftus, uses convulsive therapy to treat what he calls Helen’s schizophrenia. Helen responds poorly to the initial rounds of treatment, but Benjamin tells the doctor to keep going. The next time Helen receives the treatment, her heart gives out, and she dies. Benjamin returns to New York but is diminished by Helen’s death. He continues to invest, but he seems to have lost his previous business acumen.
In the next document, Andrew Bevel attempts to write an autobiography, and it becomes clear that Andrew is the real-life character (in the world of the novel) upon whom Benjamin Rask is based. Like Benjamin, Andrew is born to a prominent New York family. His family has been wealthy for generations, going back at least to his great-grandfather William’s fortune, which he generated by buying nonperishable goods like cotton from Southern farmers during a trade embargo in 1807.
Andrew enters into business in 1907 using formulas he developed in college. Soon after, he meets his wife, Mildred (who is Helen in Bonds). He credits her with saving his life by making a home for him. Andrew becomes even more successful after the two meet. Mildred is devoted to music and holds concerts in their new home. She becomes involved in philanthropy, but her health begins to decline. Andrew arranges for Mildred to be treated for cancer in a sanatorium in Switzerland, and he travels with her. One day, he goes to Zürich for business. When he returns to the sanatorium, Mildred has died.
Andrew also writes that his family has always believed that self-interest can go hand-in-hand with the public good. That philosophy dictates all of his business decisions, even when that might not seem to be the case, as in the Wall Street Crash of 1929, when Andrew makes a fortune while countless others go bankrupt. Because he made money during that time, the media incorrectly (from Andrew’s perspective) suggests that he might in part be to blame for what happened during the crash.
In the third document, Ida Partenza details her experience working as the ghostwriter for Andrew Bevel’s autobiography. In 1938, she and her father live together in Brooklyn and struggle to make ends meet. She applies to job after job and eventually, Andrew Bevel hires her. She thinks she’ll be his secretary, but it turns out that he wants her to help him write his autobiography. The job pays more than Ida could ever imagine, and she’s able to use the money to pay off her and her father’s debts. Ida’s father is an anarchist who immigrated from Italy to New York and doesn’t approve of Ida’s new job working on Wall Street.
Andrew explains to Ida that he wants to write his autobiography to counter the lies of Harold Vanner’s novel Bonds. He’s particularly concerned with the novel’s depiction of his late wife, Mildred, and how the novel portrayed his role in the crash of 1929. In response to the novel, Andrew buys the company that published the book and buys every copy of the book so no one can read it. He also buries Harold Vanner in lawsuits that Andrew doesn’t have any expectation of winning, but this will keep Harold Vanner occupied.
One day, a man stops Ida outside her apartment when she returns home from work. He demands that Ida give him the manuscript she’s been working on for Andrew. Ida decides to write a fictional account to give to the man and does lengthy research in the library. When she brings her fictional account to the man a few days later, it dawns on her that he’s not someone that she should be afraid of. She asks the man who he works for, and he confesses that Ida’s sometimes boyfriend, Jack, sent him. Jack is an aspiring journalist and thinks that if he can get the manuscript, he can sell it to a newspaper and use it to get a job. Ida tells the man that Andrew knows what Jack is up to, and Jack better leave town immediately or else he’ll face Andrew’s wrath. Jack leaves New York for Chicago soon after.
While Ida and Andrew work, Ida is dismayed at the way that Andrew changes Mildred’s character. He describes Mildred to Ida as supremely intelligent and drawn to avant-garde classical music, but when Ida writes that in the autobiography, Andrew tells her to take it out. He doesn’t want anyone to think Mildred was pretentious and tells Ida to portray her as childlike and gentle, which doesn’t square with Ida’s understanding of Mildred. Andrew also says that Mildred had cancer and never suffered any mental illnesses. He talks at length about how history has misunderstood his role in the 1929 crash. He wants to set the record straight on both counts. Andrew dies unexpectedly while he and Ida are still working, and the manuscript remains unfinished.
Ida goes on to become a writer. In the mid-1980s, she hears that Andrew’s house, which has been turned into a museum, has papers belonging to both Andrew and Mildred. She goes to the museum, hoping to find something that will shed light on the truth about Mildred. In Mildred’s papers, she finds a nearly impossible-to-read diary that Mildred once kept.
The fourth and final document in the book is Mildred’s diary, which Ida finds in Mildred’s papers. In the diary, Mildred details her time receiving cancer treatments in a sanatorium in Switzerland. She discusses her frustrations with Andrew and her love of avant-garde and experimental classical music. She frequently gives Andrew advice about what trades to make and documents how she masterminded the transactions that made Andrew’s fortune and reputation. She also discusses her role in the financial crisis of 1929. She saw that the stock market would crash and pushed Andrew to take out short positions, which would enable them to make a profit when the market crashed. When the crash occurred, Mildred wanted to use the profits they gained to help those impacted most by the crash, but Andrew only donated paltry sums to a few charities to try and save face. In the sanatorium, Mildred’s health gradually declines, and the diary ends, signaling Mildred’s death.