This is a short mission that will require speed from you if you wish to obtain the Gold Medal. Head over to Caliga Hall found just to the east of Rhodes and speak to the guard to let you in. You’ll find Beau Grey to the northwest of the entrance, leaning up against a shack and he’ll ask you for some help with regards to his beloved.
Quickly mount the horse and race over to Braithwaite Manor found to the southwest of Rhodes. Stop once you reach the edge of the area and go on foot, you’ll need to avoid being spotted by the guards here. You can see their field of vision on the radar and you can easily cut a path through starting from the northwest of the manor. Keep low but stay moving quickly to reach the gazebo where Penelope awaits.
If you’re replaying this mission for the Gold Medal, consider skipping the cutscene to speed things along, you’ll now need to leave the manor without being seen. Close to the gazebo is a boat, jump inside and row northwest to escape the red area on the radar and complete the mission.