How do you get past the bad guys on Counterfeit Island?

To get past the Black Widow's guards in her lair :

Go along the bottom level until you get to the end. Climb up behind the guard and get above him on the boxes. When you see the female guard (third level) walk over and turn away, jump up and sneak behind her until you get near the chair. Jumping on the springy chair should send you up and left to the locked door. (You have the key card.)