It's the 30° mission in chronological order of the RDR2 story mode, played with protagonist Arthur Morgan .
While optional for story progression, this is an Optional Honor Mission required for the "Lending a Hand" Trophy/Achievement. It's a time-sensitive and missable mission, so it can only be played at this specific point in the story.
The Course of True Love - I & II - Mission Details:
Beau Gray asks Arthur to deliver a letter to Penelope Braithwaite at Braithwaite Manor.
Gold Medal Objectives (100%)
The following are the Mission Objectives required to obtain the Gold Medal in the mission "The Course of True Love - I & II":
- Reach Penelope without getting spotted
- Complete within 3 minutes
Note: You must complete all Gold Medal requirements in one single playthrough of the mission.