A young man enters Granger Bookstore while Olivia Granger's grandfather watches.
To get his mind off things, Marlene suggests a couple's pottery class even though they're not a couple, to which Sirius thinks he sees someone who shouldn't be there as they're supposed to be dead.
That day a year ago holds a different meaning for Sirius than it does Regulus.
Regulus should have died, and then he didn't for some reason even he can't quite explain. Or perhaps he did, in a way.
Sirius gets an irrational idea into his head, but he decides to act upon said irrational idea, only to discover something.