He didn't believe that she loved him.

Helen had always been fond of her friend Sylvia, and she felt an enormous debt of gratitude towards Sylvia's mother--so she had always felt obliged to keep a protective eye on her friend, so much less self-reliant than Helen and so apt to land herself in impossible situations.

When Sylvia found herself trapped in a disastrous marriage to an impossible man -- the famous playwright Charles Lane, who according to Sylvia was selfish, tyrannical, conceited and unfaithful--it was to Helen that she turned. She persuaded Helen to help her out of the situation by tricking Charles into setting her free.

The plot the two girls worked out was fool-proof; it went without a hitch--until the very last moment, when Helen discovered to her horror that Charles Lane, the 'selfish, tyrannical husband', was the man with whom she herself had just fallen in love.