Even Grace Roseberry herself was subdued by her own presentiment of some coming interference for which she was completely unprepared.
Julian's words and actions, from the moment when he had written on the card, were involved in a mystery to which not one of the persons round him held the clew.
The motive which had animated his conduct may, nevertheless, be described in two words: Julian still held to his faith in the inbred nobility of Mercy's nature.
He had inferred, with little difficulty, from the language which Grace had used toward Mercy in his presence, that the injured woman must have taken pitiless advantage of her position at the interview which he had interrupted.

Instead of appealing to Mercy's sympathies and Mercy's sense of right--instead of accepting the expression of her sincere contrition, and encouraging her to make the completest and the speediest atonement--Grace had evidently outraged and insulted her.

As a necessary result, her endurance had given way--under her own sense of intolerable severity and intolerable wrong.
The remedy for the mischief thus done was, as Julian had first seen it, to speak privately with Grace, to soothe her by owning that his opinion of the justice of her claims had undergone a change in her favor, and then to persuade her, in her own interests, to let him carry to Mercy such expressions of apology and regret as might lead to a friendly understanding between them.
With those motives, he had made his request to be permitted to speak separately to the one and the other.

The scene that had followed, the new insult offered by Grace, and the answer which it had wrung from Mercy, had convinced him that no such interference as he had contemplated would have the slightest prospect of success.
The only remedy now left to try was the desperate remedy of letting things take their course, and trusting implicitly to Mercy's better nature for the result.
Let her see the police officer in plain clothes enter the room.

Let her understand clearly what the result of his interference would be.