Simon Peter and another disciple were following Jesus. The high priest knew the other disciple. So that disciple went with Jesus into the high priest's courtyard.
References for John 18:15
But Peter had to wait outside by the door. The other disciple came back. He was the one the high priest knew. He spoke to the woman who was on duty there. Then he brought Peter in.
The woman at the door spoke to Peter. "You are not one of Jesus' disciples, are you?" she asked him. "I am not," he replied.
It was cold. The servants and officials stood around a fire. They had made it to keep warm. Peter was also standing with them. He was warming himself.