He thought Gavin's duty was to get his father to compel Gavinia to give the book up.
Was Tommy daft?
Mr.Dishart did not know that his son possessed these books.

He did not approve of story books, and when Mrs.Dishart gave them to Gavin on his birthday she--she had told him to keep them out of his father's sight.

(Mr.and Mrs.Dishart were very fond of each other, but there were certain little matters that she thought it unnecessary to trouble him about.) So if Tommy was to get "Waverley" at once, he must discover another way.
He reflected, and then set off to Miss Ailie's (to whom he still read sober works of an evening, but novels never), looking as if he had found a way.
For some time Miss Ailie had been anxious about her red-armed maid, who had never before given pain unless by excess of willingness, as when she offered her garter to tie Miss Ailie's parcels with.

Of late, however, Gavinia had taken to blurting out disquieting questions, to the significance of which she withheld the key, such as-- "Is there ony place nowadays, ma'am, where there's tourniements?
And could an able-bodied lassie walk to them?
and what might be the charge to win in ?" Or, "Would you no like to be so michty beautiful, ma'am, that as soon as the men saw your bonny face they just up wi' you in their arms and ran ?" Or again, "What's the heaviest weight o' a woman a grand lusty man could carry in his arms as if she were an infant ?" This method of conveyance seemed to have a peculiar fascination for Gavinia, and she got herself weighed at the flesher's.

On another occasion she broke a glass candlestick, and all she said to the pieces was, "Wha carries me, wears me." This mystery was troubling the school-mistress sadly when Tommy arrived with the key to it.