Can't be found, receive a mysterious text

After a solid minute of frantic searching, Anna couldn't find where her panties had landed and sighs as the bell to end class rang out through the school. "Alright class, be sure to have problems 5 through 10 done by tomorrow!" The teacher announced as people started filing out. Anna felt completely naked sitting at her desk; the cold plastic seat pressing up against her bare bottom, hidden only by a skirt that had lost its fastener. Standing up, Anna could feel her skirt holding...but heard one "click" to indicate one link of the zipper had come undone.

"Great...what am I doing to do n-" Anna's thoughts are soon interrupted when she entered the hallway, the faint feeling of vibration being felt from her skirt. Pulling out her phone, an unknown number sent her a message, Anna reading it in her head;

"Hello, Anna. I have something of yours that you may wish to have back."

On cue, a picture message from the same number came in, showing the panties she'd lost just minutes ago, being held out by a gloved hand. Another message followed seconds later.

"I am willing to make a deal."