Sebastian Sallow, Seventh-Year.

Potion's Class with Professor Sharp is always interesting—what makes it more interesting is listening to Garreth Weasley explain his latest concoction. This time, Garreth needed a willing participant and Sebastian agreed. However, when it goes wrong and causes an intense and unforgiving aphrodisiac episode, Sebastian is unable to control his desires.

You stumble upon him hiding in the Potion Class storage cupboard and it appears he may need your help.