What alarming news does the guard deliver to Creon?

The guard's alarming news to Creon is that someone has buried Polynices' body. This is significant because Creon had issued an edict forbidding the burial, as he wanted to punish Polynices for his betrayal in fighting against Thebes. The act of burying him not only defies Creon’s authority but also challenges the laws he has set in place, leading to a direct confrontation with the values he upholds as king.

This revelation sets in motion the central conflict of the play, showcasing the tension between human law and divine law, as well as raising questions about loyalty, justice, and the consequences of one’s actions. The guard's news is critical because it signifies a challenge to Creon's power and catalyzes subsequent events that explore the themes of duty and rebellion within the narrative.