The Triangle:

Office drone C. C. Baxter (Jack Lemmon), boss Mr Sheldrake (Fred MacMurray) and elevator operator Fran Kubelik (Shirley MacLaine)

Does It Get Complicated?  

This one ought to be simple.  Baxter’s got the perfect bachelor pad for a fling.  It’s just a matter of getting Miss Kubelik there.

The catch: Baxter’s des res is common knowledge.  He’s already pimping out the place to his bosses as a base for their affairs, and Mr Sheldrake has taken note.

Soon, the problem won’t be getting Miss Kubelik into Baxter’s bed… but getting Baxter into Baxter’s bed.