It was a trap. Wait, wait, and keep waiting patiently—Harry felt himself gradually losing patience.
After obtaining that crucial memory from Professor Slughorn, Harry had only briefly returned to the Gryffindor Common Room to share the good news with Ron and Hermione before going straight to the Headmaster's Office to wait for Dumbledore's return.
However, Harry had not expected to face such a long wait.
He waited from morning until noon, then from noon until afternoon, yet Dumbledore still did not return to Hogwarts, as though the memory he had obtained was of no consequence.
Professor McGonagall visited the Headmaster's Office again and told Harry about Professor Slughorn's condition. The poor Potions Professor had successfully been cured of the Veritaserum's effects. Apart from being badly frightened, he had not suffered any serious injuries.
Harry was not surprised that Snape had an antidote to Veritaserum. Narcissa had most likely obtained her Veritaserum from Snape.
The whole thing had been rather too convenient.
If Snape had been Dumbledore's man through and through, Harry might even have suspected that this had all been a scheme devised by Dumbledore and Snape: Narcissa would use Veritaserum to force Slughorn to reveal Felix Felicis's whereabouts, then Harry would arrive and successfully reap the benefit, accomplishing an almost impossible task.
Harry could hardly be blamed for thinking that. In Albert's words: there had never been that many coincidences in this world.
Unfortunately, Dumbledore and Snape were not on the same side at all. Otherwise, Slughorn would probably have cried himself unconscious in the toilet.
After pacing around the office for who knew how many laps, ignoring Phineas's portrait as it grumbled in displeasure, Harry sat back down in the armchair and used the Marauder's Map to search for Malfoy. He kept feeling that the boy was plotting