He had given of his best to train it to its present perfection, and now he saw the fruit of his labour about to be snatched from him.

It was more than human nature could endure.
Errington meant nothing to him, Diana and her voice everything; and he was prepared to sacrifice no matter whom to secure her career as an artiste.

By implication he sacrificed Errington.
"It is not possible for me to say more.

But be advised, my dear pupil.
Out of my great love for you I say it--_let Max Errington go his way_." And with those words--sinister, warning--ringing in her ears, Diana returned to Brutton Square.
But Baroni was not content to let matters remain as they stood, trusting that his warning would do its work.

He was determined to leave no stone unturned, and he forthwith sought out Errington in his own house and deliberately broached the subject of his engagement to Diana.
Max greeted him affectionately.
"It's a long while since you honoured me with a visit," he said, shaking hands.