Charles meets with Tibby at the house at Ducie Street. The two of them have nothing at all in common, and their conversation is a travesty.
Charles is determined to get rid of Helen, who he sees as nothing but a liability.
Tibby, however, has the luxury of wealth and freedom, and he thinks that Helen should be able to do whatever she perceives to be right. His life of leisure has made him unsympathetic to the struggles of others.
Charles tries to get Tibby riled up about Helen's pregnancy, and tries to get him to admit the identity of Helen's mystery man.
Tibby, menaced by Charles, mentions that Helen had brought up the Basts before – but he says nothing else.
Charles takes this to be an admission of guilt, and assumes that Tibby aided and abetted in Helen's affair with Leonard; disgusted, he storms out.