Basic premise: three people from the present use a time portal to end up in 1888 London, Whitechapel district. The antagonist, Jonathon Avery, actually ends up there four years earlier and his mental unbalance leads him into setting up a monopoly on the newspapers with grander desires. Our heroes, Sara followed by special ops agent David arrive on the scene. But there's something not quite right going on in Whitechapel when they arrive. Jack the Ripper is at large and Sir Jay Osborne is quite the popular figure. Add in Inspector Jonas Robb for the tour guide and interactions with the Ripper cast of characters and you're off.
As a novel about time travel, it's not bad. The heroes are careful who they interact with until the end. Sara and David have differing theories on how history can be changed, one is the Chaos Theory where the slightest variation is going to effect everything and the second is a domino theory where only serious events are going to manipulate the unfolding of time. It's a subject matter that is really only debated on the surface level as many writers will do. The manner in which the author "breaks" between scenes and people was truly quite annoying at first but you will bypass this and even accept the reasons for it.
As a novel on Jack the Ripper, I enjoyed it but it could have been better. It's not hard to figure out where the author is going in terms of who Jack is. There are certain aspects of the JtR story I enjoyed much more than the time travel. One being the Osborne Charity Hospital, who's attending doctors are Michael Ostrog, George Chapman, Neil Cream, and Francis Tumblety. Those who know Ripper studies, know the significance of those names. The author includes the canonical 5 victims and the speculative other victims. Throw in a coverup of a much larger scale of murders throughout the London districts and the story becomes more intriguing. The downfall of the JtR story is there is very little "flavor text" so you really have no idea how bad Whitechapel was in 1888. You don't really get the feel and immersion into what the setting is like unless you have previous knowledge of it.
Better still for this book is the look at just how the newspapers are/were the central hub of information and how easy it can be to manipulate the public based on what is reported versus what isn't. This too me was the better story of the whole novel. The use of the media to manipulate the public, the police, and even the government into a submissive or embarassing position. There's also a pollution of the economy going on with counterfeit money which in turn will potential destabilize the government without the gold standard to back it up, and of course the "evil plot" thickens as a savior is setting up the redemption for the poverty of the political state.
Overall, as a story on the whole, 'Jack Knife' is a bit of a "What if...?" storyline with social and political commentaries mixed in. It's enjoyable but there may be just one too many subplots going on. The story takes off in the last 100 pages and the ending is satisfying although I expected a different turn out to make it a "happier ending" for the characters and some sappy readers. I'm glad it didn't work that way. So again, as a Jack the Ripper novel, it's decent enough; as a time travel novel, there's a lot of plot holes. As a story in general I appreciated it and will recommend it for the Ripperologist in you and as an overall good social commentary on how easily people at large can be manipulated.