That is a good point about the students that they might not be the most likely to be kept for detention. Perhaps for a jock character she asks him to stay after class to help with something sports related, and then from there do what she needs too. I know it goes against the 'detention' idea, but it might work. It could be a short and easy task that didn't even really need to be done, just moving something about for her in the sports stock room where afterwards she could offer a drink which has been spiked, and then store the student like you suggested.<br/><br/>What about another teacher helping to move the students to another location, you did say about other members of staff being under her control for a variety of reasons. Perhaps the sports teacher gives out an energy drink during class, 1 is drugged though, and when the student starts to feel drowsy he is led off by the teacher to a location of the headmistress' choice instead of the school nurse, the student none the wiser to how he got there, and the teacher blackmailed into silence.