It opened inwards, and had been left standing wide, by Mary Antony.

Indeed, in summer it stood open day and night, for coolness.
As the Prioress walked along the dimly lighted passage, she could see, through the open door, sheets of rain driving through the cloisters.
The storm-clouds had burst, at last, and were descending in floods.
The Prioress stood in the shelter of the doorway, looking out into the cloisters.

The only places she could not view, were the entrance to the subterranean way, and the flight of steps leading thereto.

She would have wished to examine these; but it seemed scarcely worth passing into the driving rain, now sweeping through the cloister arches.

After all, whatever possible danger lurked down those steps, the safety of the Convent would be assured if she closed this door, between the passage and the cloisters, and locked it.
Stepping back into the passage, she seized the heavy door and swung it to, noting as she did so, how far too heavy it was for the feeble arms of old Mary Antony, and deciding for the future to allot the task of closing it to a young lay-sister, leaving to Mary Antony merely the responsibility of turning the key in the lock.
This the Prioress was herself proceeding to do, when something impelled her to turn her eyes to the angle of wall laid bare by the closing of the door.
In that dark corner, motionless, with shrouded face, stood a tall figure, garbed in the dress of the nuns of the Order of the White Ladies of Worcester.
Perhaps the habit of silence is never of greater value than in moments of sudden shock and horror.
One cry from the Prioress would have meant the instant opening of many doors, and the arrival, on flying feet, of a score of frightened nuns.
Instead of screaming, the Prioress stood silent and perfectly still; while every pulse in her body ceased beating, during one moment of uncontrollable, cold horror.