The Magical Pony #5: A Fun Birthday

Vigga is going to a party at the public swimming pool.
It’s a birthday party for her new classmate, Dagmar.
She brings Luna, but keeps her in the dressing room, because she doesn’t want the other kids to see her.
Vigga, Anker and Dagmar start playing together, but soon, some of the older boys try to spoil the fun.
Where’s Luna and what is she up to?