Tom is the twenty-one year-old who works at the auto insurance agency with the teenaged Slocum. Slocum is fascinated by Tom's relationship with Marie Jencks and wishes he could go at it with Virginia in the storeroom in the same way that Tom and Marie do. Slocum lives vicariously through Tom to the point that he "borrows" Tom's handwriting and never gives it back.
Mrs. Yerger is the old secretary at the auto insurance agency where Slocum worked as a teenager. Though she is likely long gone, she continues to haunt Slocum. It's because of her that he hates and fears older women who are superstitious and forcefully opinionated, like Derek's new nurse.
Martha is a typist in Slocum's department who is slowly going crazy. She makes people quite nervous and uncomfortable, perhaps because she's a symbol of how crazy their world is under the surface. At the end of the book, when Slocum ascends to Kagle's position, he escorts Martha out with grace before she can do anything to embarrass herself or the company.
Penny is a thirty-two-year-old mistress Slocum has been going with for nearly ten years. They're not in love with each other, nor have they ever been. There're just in it for the sex.
Slocum predicts that Penny will likely remain single her whole life and will therefore entertain suicidal thoughts, much as Virginia did. Slocum sort of understands how awful this position is, and he says that hopes his daughter will not end up like Penny, going around with other women's husbands.
Another employee at Slocum's company, Red Parker has been a widower for almost too long a time now, and he'll soon get in trouble for it: apparently he is having too good a time being single, and the company is taking note. Don't rock to boat in this society, folks. It's in Red Parker's Manhattan apartment, of course, that men in the office, like Slocum, go to have their affairs.