Discipline was savage. Like other captains, Nathan Rawson warned his troops that if anyone disturbed the army's silent progress through the dark, he would be killed on the spot by his neighbour. The four thousand men who left their camp at Castle Field did not even dare to whisper. Instead of heading for the enemy in a direct line, they opted for a circuitous march six miles in length that would allow them to strike at the northern flank of the royal camp. Following the Bristol road, they reached Peasey Farm, where they left their baggage train, continuing their advance until they got to the Langmoor Rhine.

It was here that the plan faltered. In the swirling fog, the local man acting as their guide could not find the crossing that had been cut into the deep ditch. As he beat round in search of it, he was heard by an alert sentry on the other side of the Rhine. The man also picked up the sound of jingling harness and the shuffling of hooves in the grass. Firing his pistol to warn the patrol at Chedzoy, he galloped all the way back to the bank of the Bussex Rhine and raised the royal camp with shouts of "Beat the drums, the enemy is come! For the Lord's sake, beat the drums!"

The battle of Sedgemoor had begun. When the alarm was sounded, the response was immediate. The royal army was not, in fact, lying in the drunken stupor on which the rebels had counted. It was ready for action within minutes. Seizing their weapons, the soldiers deployed between the tents and the Bussex Rhine in good order, helped by the fact that tapes had been strung out in advance to act as guide ropes in the darkness. They met the sudden emergency as if they had been expecting it.

The rebel infantry was still a mile from the royal camp but the cavalry had no need to hold back. Thundering across the moor, they headed for the Upper Plungeon, one of the cattle crossings in the Bussex Rhine. On their way, they were met by a sizeable mounted picket as it fell back towards the royal camp.