He collected as many keys as he could, and tried all of them during one of those delightful hours which Rosa and Cornelius passed together at the grating of the cell.
Two of the keys entered the lock, and one of them turned round once, but not the second time.
There was, therefore, only a little to be done to this key.
Boxtel covered it with a slight coat of wax, and when he thus renewed the experiment, the obstacle which prevented the key from being turned a second time left its impression on the wax.
It cost Boxtel two days more to bring his key to perfection, with the aid of a small file.
Rosa's door thus opened without noise and without difficulty, and Boxtel found himself in her room alone with the tulip.
The first guilty act of Boxtel had been to climb over a wall in order to dig up the tulip; the second, to introduce himself into the dry-room of Cornelius, through an open window; and the third, to enter Rosa's room by means of a false key.
Thus envy urged Boxtel on with rapid steps in the career of crime.
Boxtel, as we have said, was alone with the tulip.
A common thief would have taken the pot under his arm, and carried it off.
But Boxtel was not a common thief, and he reflected.
It was not yet certain, although very probable, that the tulip would flower black; if, therefore, he stole it now, he not only might be committing a useless crime, but also the theft might be discovered in the time which must elapse until the flower should open.
He therefore--as being in possession of the key, he might enter Rosa's chamber whenever he liked--thought it better to wait and to take it either an hour before or after opening, and to start on the instant to Haarlem, where the tulip would be before the judges of the committee before any one else could put in a reclamation.
Should any one then reclaim it, Boxtel would in his turn charge him or her with theft.
This was a deep-laid scheme, and quite worthy of its author.
Thus, every evening during that delightful hour which the two lovers passed together at the grated window, Boxtel entered Rosa's chamber to watch the progress which the black tulip had made towards flowering.
On the evening at which we have arrived he was going to enter according to custom; but the two lovers, as we have seen, only exchanged a few words before Cornelius sent Rosa back to watch over the tulip.
Seeing Rosa enter her room ten minutes after she had left it, Boxtel guessed that the tulip had opened, or was about to open.
During that night, therefore, the great blow was to be struck.

Boxtel presented himself before Gryphus with a double supply of Genievre, that is to say, with a bottle in each pocket.
Gryphus being once fuddled, Boxtel was very nearly master of the house.
At eleven o'clock Gryphus was dead drunk.

At two in the morning Boxtel saw Rosa leaving the chamber; but evidently she held in her arms something which she carried with great care.
He did not doubt that this was the black tulip which was in flower.
But what was she going to do with it?
Would she set out that instant to Haarlem with it?
It was not possible that a young girl should undertake such a journey alone during the night.
Was she only going to show the tulip to Cornelius?
This was more likely.
He followed Rosa in his stocking feet, walking on tiptoe.
He saw her approach the grated window.

He heard her calling Cornelius.
By the light of the dark lantern he saw the tulip open, and black as the night in which he was hidden.
He heard the plan concerted between Cornelius and Rosa to send a messenger to Haarlem.

He saw the lips of the lovers meet, and then heard Cornelius send Rosa away.
He saw Rosa extinguish the light and return to her chamber.