-I can't say for certain, because it all depends—well, it all depends upon a factor which is completely outside our control. But I have great hopes—in fact, the betting is exactly two to one—that if you will come with us to-night I shall be able to help you to lay him by the heels."
Does it mean
1. It is very likely that we will win
2. we are as likely to win as we are to lose?
The idea is that they have a reasonable chance of winning. It is not a "long shot." 2-1 odds in a horse race are fairly good. It means you would win $2 for every $1 bet.
A 10-1 or 20-1 bet would be much less likely to be a winner.