Star Trek: Deep Space Nine: Hollow Men is a direct sequel to the episode "In the Pale Moonlight."
For those of you who haven't seen that episode, I suggest you stop reading and go watch it now. It's one of the best episodes of Star Trek I've ever seen and I've seen a lot of them. It also is one of the most highly controversial and morally troubling episodes. Not morally troubling the way, "Dear Doctor" is but calling into question your own values. I'm going to spoil the episode if you read further, so consider yourself warned.
The premise of "In the Pale Moonlight" is Captain Sisko and Garrak attempt to bring the Romulans into the war against the Dominion by faking plans of an invasion. It's, already, morally troubling to an absurd degree. This is equivalent to faking an invasion of Latveria to make sure they join up against the Nazis. Yes, the Nazis have it coming but this is a fight which will lead to the death of many Latverians. Admittedly, Doctor Doom probably wouldn't care but that just goes to show he's a horrible leader.
Things get worse for Sisko as the plan goes pear-shaped and they end up having to murder a Romulan Senator as well as his pilot (not to mention their forger) in order to make sure the plan goes off without a hitch. In the end, the Romulans enter the Dominion War on the side of the Federation and it gives "our" side some much needed breathing room. Sisko is left with the troubling question of whether he can live with himself. The answer from the episode? Yes, yes he can.
This book analyzes if he was kidding himself. Sisko returns to Earth and Starfleet Headquarters for a conference on the Dominion War. Both Garak and their new Romulan allies will be present at this occasion. Sisko, determined to thine own self be true, has decided to fess up to his role in the conflict to his superiors. It's a stark contrast to his behavior at the end of the episode and could have made him look week but struck me as an appropriate response to a man trying to bury his guilt. The idea Sisko wants to be punished for not only his murders but the potentially thousands of Romulan deaths he'll cause is a pretty decent one.
This part of the book is good, very good in fact. Unfortunately, it only compromises about a quarter of the book. Una McCormack, perhaps realizing that there's not much suspense in Captain Sisko's future (we know he and Garak keep their relative positions after all), instead attempts to create a number of subplots to keep the novel going.
One of these B-stories, a heist of latnium on Deep Space Nine, flat-out didn't interest me. The plot with a former Starfleet intelligence officer turned peace protestor is good but doesn't end in a satisfying manner. I didn't grasp the character's motivations until the end of the book and the tie-in with a certain group of baddies I normally appreciate just didn't work.
Star Trek: Deep Space Nine: Hollow Men is at its best when it's questioning the nature of guilt and what sort of actions we're willing to do in order to achieve victory. Also, the question of whether or not peace with evil enemies is a viable choice of action if it means preserving your way of life. Sisko is confronted with the rather ambiguous answer to, "is it worth it to compromise your principles to achieve victory" with the answer, "if you don't, you will lose, but if you do too often, you will lose too." It's a very true to life answer.
In conclusion, I think this was an okay book but the subplots simply didn't interest me. The original characters were okay but the novel would have been superior if we'd kept a focus on Garak and Sisko. I suggest you pick it up if you're a fan of the episode but don't expect anything game-changing. The book is too limited by continuity, I'm sorry to say.