A man races against time to save his fiance on the 74th floor of the South Tower on 9/11.

These Irwin Allen type stories need little else unless you have something special.

My 'vijf cent'
You can change "man" for an other more powerful word that describes the man, if that's even possible. For so far:

A adulteress man races against time to save his fiance on the 74th floor of the South Tower on 9/11.

Get back later...

I quite like this, we've got most ingredients needed, but can you expand on "man". Give him a flaw which makes it even more incrediable. A man suffering from vertigo must... A hopeless romantic... A man scared of commitment...
Give him a voice. Make the task even more unatainiable. We know the towers will fall, but what is his internal battle? What does he need to overcome to save his love? Is 74 floors all there is? Or is it 74 floors of doubt?