This event is automatically triggered on the Sententae holiday at the end of the second week of Nivelos.
1. Sleuthing vs 7 - Try to figure out who could be playing a joke on you.
Success - Unlock option 2, select another option. Failure - No effect, select another option.
2. Playfulness vs 4 - Find the culprit.
3. Magical Appraisal vs 4 - Cast a spell to make the message disappear.
Success - Flawless Timing +1 SS Failure - Stress +1
4. Get out of there quickly.
Automatic - Diplomacy +1 SS
Note: Option 2 really have the reward for failing rather than succeeding. Based on the text, it appears deliberate.