[Quick Summary: After a con woman and a rich, gullible ophiologist (a snake scientist) fall in love and split up, she disguises herself as English aristocracy to dupe him once more.]
Farce is a tough genre. It's just too easy to go too far with the satirical comedy or improbable plots.
So why does it work here?
According to Roger Ebert, this story avoids the mistake of many films and gives a "baseline of sanity to measure the characters against....Henry Fonda is the rock."
Fonda is the gullible (but not stupid) snake scientist. He doesn't want to use Barbara Stanwyck for his career. He's sincere and earnest as he pursues her. He's puzzled by the "coincidences" but chalks it up to feeling more alive just by being with her. He's truly, madly, crazy in love.
So when he doesn't realize Barbara's dad is blatantly hustling him at cards, we believe him.
When he "happens" to get a photo showing Barbara is a con, we're crushed along with him.
When Barbara creates an English persona and Fonda does not recognize her AT ALL, it all makes sense.
We believe in Fonda, even if everything else is truly preposterous.
WHAT I'VE LEARNED: Farce can be way, way over the top - but only if there's at least one person who makes it feel real.
Lady Eve (1941)
by Preston Sturges