The Princess of Convenient Plot Devices, Vol. 4 (light novel) — Mamecyoro

The night of the junior ball ended with a well-earned victory, and the sun rose on a princess…under house arrest?! Prince Sirius has Octavia on lockdown for endangering herself, and though she does her best to plead her case, convincing her brother won't be easy. He also has Klifford detained on suspicions of orchestrating Sil's carriage accident. It's Octavia's turn to defend her guard, but can she prove his innocence in time? Danger is around every corner -- the anti-royalists aren't done with her yet!