Rofflash knew of more than one infamous den to which Lavinia could be conveyed, and nobody be the wiser.
The abduction plot had failed--for the present--and Rofflash, to pacify Dorrimore, went on another tack.

In this he was personally interested.
He saw his way to make use of Dorrimore to punish Vane for the humiliation Vane had cast upon him when they encountered each other on London Bridge.

This humiliation was a double one.

Vane had not merely knocked him down, but had rescued Lavinia under his very nose.
The insult could only be washed out in blood, and the captain had been nursing his wrath ever since.

But he was as great a coward as he was a braggart, and a fair fight was not to his taste.