Taxi - Tuxedo (Book 6‪)‬

Carmen unexpectedly receives tickets for the opera. She'd love to go, but she isn't sure if she can persuade Ulrike to accompany her.
Ulrike doesn't fancy operas, and she is quite relieved when she realises that she has an excuse not to go. When Carmen finds a solution for her excuse, Ulrike grudgingly agrees to go, but at the last moment she comes up with a condition that she believes her partner will never accept - that she may wear a tuxedo.
Taxi - Tuxedo is the 6th book in the Taxi series.