Simon Peter and another disciple followed Jesus. Because this other disciple was known to the high priest, he went with Jesus into the high priest's courtyard.
References for John 18:15
However, Peter stood outside near the gate. Then the other disciple (the one known to the high priest) came out and spoke to the woman stationed at the gate, and she brought Peter in.
The servant woman stationed at the gate asked Peter, "Aren't you one of this man's disciples?" "I'm not," he replied.
The servants and the guards had made a fire because it was cold. They were standing around it, warming themselves. Peter joined them there, standing by the fire and warming himself.