Isabelle is involved with four men over the course of the novel, The Thinking Reed. Who are they?

Isabelle, an American from St. Louis, lives in France and in the course of the novel becomes involved with four different men: Laurence Vernon, an American whom she nearly marries; Andre de Verniers, a French aristocrat who is completely corrupt and decadent; Marc Sallafranque, an automobile manufacturer as corrupt as de Verviers; and Alan Fielding, an English painter who befriends her when her marriage to Marc breaks up after she miscarries her child.