The Mysterious Stranger at the Party

You and your partner decide to attend a masquerade party separately. You don't know each other's costumes, adding a thrill of mystery to your evening. You meet a plethora of interesting 'strangers.' In a turn of destiny, you end up meeting the most enchanting stranger of them all - your partner. However, the whole purpose of the roleplay is not to recognize each other. Flirt, dance, and engage in subtle, naughty conversations, creating an aura of unexpected romance.
The scenario heightens with secretive exchanges and stolen glances. Your conversations are intriguing and filled with sexual innuendos. As the night deepens, the stranger (your partner) suggests a more secluded spot, away from the party's frenzy.
The secluded spot is your home. What was initially a party has now turned into an intimate scenario with just the two of you. The narrative progresses in the comfort of your home where you continue with the sensual, passionate play.

Plan your masquerade party. This could be a simple setting at your home or a rented, but it should be decorated with dim yet colorful lighting. Arrange for masquerade masks and costumes that you won't reveal to each other beforehand.
Next, plan your conversations and actions. The trick lies in not acknowledging your partner but being enchanted by the stranger they are portraying. Be prepared for the sexual tension that will naturally build between you two as strangers.
Lastly, arrange some background music and wines that will set the mood for the scenario.

Add some elements of surprise in your conversations as strangers. You can pretend to be completely different characters, ones you have aspired to be, or ones your partner would like. This will keep the scenario compelling and mysterious.
Keep a safe word for the scenario. While roleplaying, especially in a kinky narrative, it is essential to ensure both parties are comfortable with the play's extent. The safe word will guide you both on when to stop.
Since your partner is shy, be patient and understanding. Even if it takes time for them to come into character, encourage them subtly, assuring them that they are doing a good job.