Finally there is a third promise in these opening sentences of Sir Launcelot Greaves.

"The great northern road!" It was that over which the youthful Smollett made his way to London in 1739; it was that over which, less than nine years later, he sent us travelling in company with Random and Strap and the queer people whom they met on their way.

And so there is the promise that Smollett, after his departure in Count Fathom from the field of personal experience which erstwhile he cultivated so successfully, has returned to see if the ground will yield him another rich harvest.
Though it must be admitted that in Sir Launcelot Greaves his labours were but partially successful, yet the story possesses a good deal of the lively verisimilitude which Fathom lacked.

The very first page, as we have seen, shows that its inns are going to be real.

So, too, are most of its highway adventures, and also its portion of those prison scenes of which Smollett seems to have been so fond.