Complex sentence: They are invited to perform at the Castle of the Count des Étiquettes, who is André's uncle, but Malicorne happens to be there as well and recognised them and want them arrested on the pretext they own him money.
Split into simpler sentences: They are invited to perform at the Castle of the Count des Étiquettes, who is André's uncle. However, Malicorne happens to be there as well, recognises them and want them arrested on the pretext they own him money.