Severus Snape was discovered to be a spy by Voldemort shortly after his resurrection, and was saved by a dissolutioned Lucius Malfoy. Now joint No.1 on Voldie's shit list, they're stuck at Hogwarts and bored out of their skulls. During a maudlin drinking session, they decide to try to get rid of their Dark Marks. Snape has confiscated a tattooist's business card form one of his Muggleborn students - and, completely smashed, they decide to get a tattoo to cover up the Marks and apparate to muggle Glasgow, into the parlour where Cat Duncan, the owner of the business card, works.
All poor Cat wants to do is get a mocha and go home, now she's got two drunk wizards on her hands. Fortunately, Cat knows about wizards as the student Snape took the card from is her little brother. Unfortunately, something has begun to block all forms of magical transport, and it's up to Cat to try and get Snape and Malfoy back to Hogwarts as quickly and secretly as possible, without Voldemort finding out...