The essential tension, running throughout A Doll's House comes from Nora's fear of a secret being discovered. Her absolute terror of this revelation leads her to tell lie after lie. When her web of lies finally caves in around her, her marriage proves too weak to bear the strain.
It is ironic that Krogstad uses deceitful methods in an attempt to regain his good reputation.
Nora's lying is the only tool society has left her. She must manipulate the truth in order to have any power at all.