Much of what Mary Trump reveals in TOO MUCH AND NEVER ENOUGH has already been said during her interviews.
Most of the book centers on what Fred Sr. did to Mary's father, known as Freddie in the family. Fred had been grooming Freddie to take over the business, but Freddie just wasn't tough-minded enough. Freddie loved flying and got in on the ground floor when Howard Hughes's TWA took off, but his drinking eventually nixed that outlet. Fred never forgave him and Freddie died at age 42 of alcohol related heart failure. According to Mary, Fred saw himself in his number two son, who was self-promoting and “brash” as the press tagged him. Mary insists he was really a fraud in every respect, that Fred enabled him. Fred had concentrated on Brooklyn; he needed Donald, who was very press conscious, to get a foot in the door in Manhattan. Donald's two great successes, the Hyatt and Trump Tower, were really possible only because of Fred's tax finagling and other connections. She points to Trump's failures in Atlantic City. One casino was not enough; he built two more, but he didn't understand that they were competing against each other. Fred knew nothing about casinos, and the only way he could help him was to buy chips he would never use.
Towards the end of the book, she finally throws a bomb. Fred died in 1999, and according to his will, Mary and Fritz, Freddie's two kids were cut off. Fred's business manager recommended a lawyer as Freddie had owned twenty percent of Fred's rental business. Donald, Maryanne, Elizabeth and Rob, Fred's remaining children insisted Fred's properties were only worth thirty million, and Mary and Fritz's lawyer seemed to agree. Something stinks in Denmark. It did; Donald eventually insisted they sell that cash cow, and it sold for $700,000,000. Donald got $170 million. Do the math. How much would Freddie be owed? Sounds like fraud, right? Eventually Mary would give THE NEW YORK TIMES Donald's tax records from the settlement, and Maryanne, who was now a judge, had to resign her position, but she still got a fat pension.
Basically what Mary hammers away at is that The Donald is just doing as president what he's always done: self promotion, lying, seeking revenge from anybody who doesn't kowtow to him and lying almost every time he opens his mouth, but she doesn't mention 18-20,000 lies as we've been hearing from Washington Post fact checkers.