How could he declare the true Grace Roseberry to be mad?
How could he give the true Grace Roseberry into custody?
On the other hand, he had personally pledged himself (when the circumstances appeared to require it) to place the means of legal protection from insult and annoyance at his aunt's disposal.

And now, there stood Lady Janet, unaccustomed to have her wishes disregarded by anybody, with her band extended, waiting for the card! What was to be done?
The one way out of the difficulty appeared to be to submit for the moment.

If he succeeded in discovering the missing woman, he could easily take care that she should be subjected to no needless indignity.

If she contrived to slip into the house in his absence, he could provide against that contingency by sending a second card privately to the police station, forbidding the officer to stir in the affair until he had received further orders.

Julian made one stipulation only before he handed his card to his aunt.
"You will not use this, I am sure, without positive and pressing necessity," he said.