A frazzled man's secret lives are set to collide when he discovers his wife has invited everyone he knows to his surprise 40th birthday.

Cautious flag: You would also need to justify the motivation of the party goers, to make it seem plausible and have an audience feeling the unbearable pain of watching him suffer.

It may seem thin if they are just their to serve his story.

Someone who knows they shouldn't be there, like a mistress, probably wouldn't go, unless you write it in a way that can make feel viable.

An example of it working would be the mistress of the chilean miner, who turned up to the vigil whilst he was trapped. The stakes need to be high.

could be hilarious.

The promise of this movie is based on a secret we are not let in on. This never works.

What we do know is that this man finds out he gets a surprise party. Big deal.

What should the viewer expect to see in Act 2? Is this a comedy? Then what is our hero's main problem during Act 2? What does he try to achieve or prevent?

We need to know more.

Superficially this story smacks of a Woody Allen-esque comedy of errors, but I sense an insidious quality to this logline. Is this your intention? Has the wife discovered this secret lives and this is her way of unravelling his world in a very public, embarrassing fashion? Why is he frazzled? This feels like only half the story - half a logline. We need to know more. Is it a black comedy? Is it a thriller? A lot of the language you're using, 'frazzled', 'secret', 'collide' all set different tones.