It's been a full couple of days for Cal; the weather is bad at home and things at Milliways have been eventful. His primary concern at the moment is Hermione, and doing what he can for her. After his visit to her cell, he'd decided that part of that involved talking to Tom Riddle. Nothing confrontational, just - sounding him out. Making sure that his initial impression of the man as being a decent kind of person, not setting off any alarms for Cal, was correct.

So he's in Milliways as he has been for a little while now, half watching for Riddle and half sunk into thought.