This was a cute, but rather insubstantial, play about the achievement of peace during the Peloponnesian War.
In the late 420s BC, the Athenian pro-war statesman, Cleon, is dead, and so is Brasidas, the major Spartan commander, with both having died at the Battle of Amphipolis. There is no longer any obvious obstacle in the way of peace, and so a treaty is signed (the so-called Peace of Nicias). The Peloponnesian War and a strong anti-Cleon sentiment had dominated Aristophanes' career up until this point, and this play represents a celebration of the return of peace to Greece.
The play involves a man, Trygaeus, flying up to the gods on a dung beetle and rescuing Peace, who had been replaced by Zeus with War as being in charge of the Greeks. Trygaeus is successful, and celebrations ensue. The major comedic element comes from the usual Aristophanic "unexpected visitors" towards the end, as various people drop in to complain about the return of Peace, such as arms-dealers. And there is a sense that the Athenians have lost so many worthwhile opportunities due to the war that peace will be kind of sad, now that they have to confront the reality of what they lost.
It's fun to read a play about such an important moment in Athenian history, after having read so many plays from Aristophanes about the damage of the war (such as *Lysistrata*) but frankly, it just isn't that great; there isn't really much here. But it's nice and fun.