The Caro-Kann is a solid defense to 1 e4. It begins with 1 e4 c6 2 d4 d5 (yes, those who have second thoughts with Black after seeing the almost inevitable 2 d4 can still change their minds and play 2...d6, switching to a Pirc, but that's another story).
Gallagher leads us through the main lines we need to know to play this defense, as well as to decide what to play against it with White. We begin with the Classical: 1 e4 c6 2 d4 d5 3 Nc3 dxe4 4 Nxe4. And I agree with the author that those interested in this ought to buy Tal's book on his 1960 match versus Botvinnik as well. Black has a choice of 4...Bf5, which is fairly solid, or 4...Nd7, which can be a little trickier, or the more dubious 4...Nf6. The Classical lines take up over half the book.
Then we proceed to the Advance Variation (1 e4 c6 2 d4 d5 3 e5). Gallagher spends quite a bit of time on 3...c5 here. In this, Black is playing an Advance Variation of the French defense a tempo down. We also see a good analysis of 3...Bf5 4 Nc3, where White hopes to launch a kingside attack that includes g4 as a tempo-gaining shot at that f5 Bishop.
Next is the Panov (1 e4 c6 2 d4 d5 3 exd5 cxd5 4 c4). This is my favorite for White. That's because I can use this analysis to play White against the Scandinavian, the Queen's Gambit Declined (if I open 1 d4), and even the Nimzo-Indian (the same isolated queen pawn position can arise in all of these). After 4...Nf6 5 Nc3 e6 6 Nf3 Be7 7 cxd5 Nxd5, we're there (the author now recommends 8 Bd3). Gallagher talks about that isolated White Queen pawn, and how minor piece trades tend to favor Black here by reducing White's attacking chances.
Late in the book, there is a section on the move 2 c4, which I think Gallagher ought to have given a little more discussion. This is an attempt by White to get to a Panov before committing to playing d4. The idea is to make it harder for Black to employ certain defences (such as 5...g6) that might otherwise be used versus the Panov. After 1 e4 c6 2 c4 (I agree with Gallagher that this move looks ugly, leaving that awful hole on d4), I think Black ought to be considering 2...e5, and Gallagher gives a couple of brief ideas here. However, Black is often content to get into a Panov with 2...d5. Next is 3 exd5, to which the author gives 3...cxd5 as the automatic response. But I disagree. I think the automatic response ought to be 3...Nf6!? After that, White will have to humbly crawl back into the Panov with 4 d4, and let Black defend against it any way she wants to. Or else "win" Black's pawn with 4 dxc6 Nxc6, but this is a well-known position from the Scandinavian, and most folks would already prefer Black.
After 1 e4 c6 2 c4 d5 3 exd5 cxd5 4 cxd5 Nf6, I think White is getting what she wants after 5 Nc3, and she even has the option of playing 5 Bb5+ instead.
This book also has three pages on the Exchange Variation (1 e4 c6 2 d4 d5 3 exd5 cxd5 4 Bd3). And it has a section on the infamous Fantasy Variation (1 e4 c6 2 d4 d5 3 f3). I once fell into a famous trap in this line that Gallagher boasts he won three games in as White. I, and Gallagher's opponents, played the following first nine suicidal moves as Black:
1 e4 c6 2 d4 d5 3 f3 dxe4 4 fxe4 e5 5 Nf3 exd4? 6 Bc4 Bb4+? 7 c3 dxc3 8 Bxf7+ (this wins by force) Kxf7 9 Qxd8 cxb2+ 10 Ke2 bxc1=N+ (as the book shows, 10...bxa1=Q gets Black mated, so I tried something else) 11 Rxc1 (White's advantage is overwhelming but now my opponent demonstrates that with bad enough play, any position can be compromised) 11...Bg4 12 Qc7+ Nd7 13 Qxb7 Rb8 14 Qxa7 Nc7 15 Nc3 Bc5 16 Qc7 Rb2+ 17 Ke1 Rxg2 18 Qf4+ Ke8 19 Rab1 Rf8 20 Rb8+ Nxb8 21 Qxb8+ Bc8 22 Ne5 Bf2+ 23 White Resigns
This book is very readable and clear, and I think it is an excellent introduction to the Caro-Kann. I recommend it.