door out of which streamed a wide band of light that flung itself across
the pavement.

Down the street came two girls in poke bonnets and hurried in at the open
door. The figure drew back and was motionless as they passed, then with a
swift furtive glance in either direction a head came cautiously out from
the shadow and darted a look after the two lassies, watched till they were
out of sight, and a form slid into the doorway, winding about the turning
like a serpent, as if the way were well planned, and slipped out of sight
in a dark corner under the stairway.

Half an hour or perhaps an hour passed, and one or two hurrying forms came
in at the door and sped up the stairs from some errand of mercy; then the
night watchman came and fastened the door and went away again, out
somewhere through a back room.

The interloper was instantly on the alert, darting out of its hiding
place, and slipping noiselessly up the stairs as quietly as the shadow it
imitated; pausing to listen with anxious mien, stepping as a cloud might
have stepped with no creak of stairway or sound of going at all.

Up, up, up and up again, it darted, till it came to the very top, pausing
to look sharply at a gleam of light under a door of some student not yet
asleep.

From under the dark cloak slid a hand with something in it. Silently it
worked, swiftly, pouring a few drops here, a few drops there, of some
colorless, odorless matter, smearing a spot on the stair railing, another
across from it on the wall, a little on the floor beyond, a touch on the
window seat at the end of the hall, some more on down the stairs.