Snape crossed the corridor, his wand at the ready. He saw no one, but that was no guarantee he was safe. His heart thrummed, and he prepared to use Silencio or Obliviate if he must.

Potter had discovered one of his secrets, and soon his colleagues were whispering while glancing his direction. His Slytherin instincts led his suspicions to the worst possible conclusion.

He didn't drop his guard until he reached his quarters. He realized his mistake the moment he opened the door. A flash of light blinded him, and a roar of sound assaulted his ears:

"Happy Birthday, Severus!"