Lupine and the Unbreakable Vow (48. Unbreakable Vow)

The troublesome trio were at it again, planning a wild and
whoolly escapade. James wanted to use a series of spells
to create havock at Slitheryn House during exams. Sirius agreed,
but wanted the spells to focus more on Severus than
the other Slytherin Members. Remus was apprehensive about focusing on
the entire house at once, and tended to agree with
Sirius, that they should focus on one particular member. James
was always pushing the envelope!

They were hiding in a broom closet, planning to cast spells
in secret willy nilly so none would know it was
them. They hadn't counted on Slytherin House having a secret meeting
that night, there were too many of the oldest students
in the room for them to do what they'd planned-
they were bound to get caught. Among those present were
Lucious and Severus....they overheard bits and pieces, their collective
ears perked up when they heard the phrase 'Unbreakable Vow"
spoken by Lucious.