Stage directions show Taurus with Caesar’s army and Canidius with Antony’s army as they both cross paths. We can hear the battle off-stage, but Enobarbus comes in to deliver the horrifying news: in the middle of the battle, just when fortune could have gone one way or the other, Cleopatra’s ship turned sail and ran away.
Antony, seeing her flee, also turned his sails and followed her, leaving the battle to ruins and his honor to mockery.
Canidius enters, announcing that this defeat was due to Antony not being remotely noble.
Canidius decides to defect to Caesar’s side with his troops, and Enobarbus leans toward defecting also, though he’s not too happy about it.