Then he lightly turned the key.

He could hear Juliet fumbling at the lock.

"What is the matter ?" she called through.
"The lock has got hampered in some way," said Jennings, rattling the key, "one moment, I'll look at it carefully." As he said this he made one bound to the chair upon which she had been standing and reached his hand to the cornice at which she had looked.
Passing his hand rapidly along it came into contact with an object long and sharp.

He drew it down.

It was a brand-new knife of the sort called bowie.