The Princess in black and the perfect princess party

On spine: -2 -Today is Princess Magnolia's birthday party, and she wants everything to be perfect. But just as her guests are arriving ... Brring! Brring! The monster alarm! Princess Magnolia runs to the broom closet, ditches her frilly clothes, and becomes the Princess in Black! She rushes to the goat pasture, defeats the monster, and returns to the castle before her guests discover her secret. But every time Princess Magnolia is about to open her presents, the monster alarm rings again. And every time she rushes back

an inside-out dress here, a missing shoe there

it gets harder to keep the other princesses from being suspicious. Don't those monsters understand that now is not a good time for an attack?