Tom was too careless, and Mary too indulgent.

It was hard enough to restrain the boy during the lesson hours, falsely so called.
After that he was allowed to go where he liked, and even his mother sometimes felt relieved by his absence; so that he was continually in the men's huts, listening to their yarns--sometimes harmless bush adventures, sometimes, perhaps, ribald stories which he could not understand; but one day Tom Troubridge coming by the hut looked in quietly, and saw master Charles smoking a black pipe, (he was not more than fourteen,) and heard such a conversation going on that he advanced suddenly upon them, and ordered the boy home in a sterner tone than he had ever used to him before, and looked out of the door till he had disappeared.

Then he turned round to the men.
There were three of them, all convicts, one of whom, the one he had heard talking when he came in, was a large, desperate-looking fellow.
When these men mean to deprecate your anger, I have remarked they always look you blankly in the face; but if they mean to defy you and be impudent, they never look at you, but always begin fumbling and fidgetting with something.

So when Tom saw that the big man before mentioned (Daniel Harvey by name) was stooping down before the fire, he knew he was going to have a row, and waited.
"So boss," began the ruffian, not looking at him, "we ain't fit company for the likes of that kinchin,--eh ?" "You're not fit company for any man except the hangman," said Tom, looking more like six-foot-six than six-foot-three.
"Oh my---- (colonial oath!)" said the other; "oh my---- 'cabbage tree!' So there's going to be a coil about that scrubby little myrnonger; eh?
Don't you fret your bingy; boss; he'll be as good a man as his father yet." For an instant a dark shadow passed over Tom's face.
"So," he thought, "these fellows know all about George Hawker, eh?
Well, never mind; what odds if they do ?" And then he said aloud, turning round on Harvey, "Look you here, you dog; if I ever hear of your talking in that style before that boy, or any other boy, by George I'll twist your head off!" He advanced towards him, as if to perform that feat on the spot; in a moment the convict had snatched his knife from his belt and rushed upon him.
Very suddenly indeed; but not quite quick enough to take the champion of Devon by surprise.

Ere he was well within reach Tom had seized the hand that held the knife, and with a backward kick of his left foot sent the embryo assassin sprawling on his back on the top of the fire, whence Tom dragged him by his heels, far more astonished than burnt.
The other two men had, meanwhile, sat taking no notice, or seeming to take none, of the disturbance.