Technically, the Infernal Devices Trilogy is a prequel to The Mortal Instruments series that Cassandra Clare had written previously (although she did not completely finish the series by the time Infernal Devices came out). The reason it is termed a prequel is that although it has completely different characters, the "world" of the Mortal Instruments and Infernal Devices is the same, plus it is inferred that characters in The Mortal Instruments series are descendants of the characters in the Infernal Devices trilogy. Before I go into the "world", which I somewhat explained with the list of supernatural beings in the first paragraph, I want to make one more note of what "steampunk" means. You can certainly view the Wikipedia entry for steampunk to get a clear explanation, and I suggest that you do, because my definition is going to be very short and limited. Steampunk is a subgenre of science fiction, and usually takes places (time-wise and setting-wise) in Victorian England or the Old American West. The reason it is in the science fiction genre is that although the time period is usually nineteenth-century, twenty-first century gadgets or machinery are being used and are usually a main part of the plot. Cassandra Clare kicks this series up a notch from a "typical" steampunk by adding in the supernatural elements.
The Infernal Devices take place in Victorian London, in the latter-half of the 1800's. The meat of this story is in describing the world that Clare has built. A long time ago, in this world, an Angel mixed his blood with that of man, and the Nephilim (Shadowhunters) were born. Shadowhunters are those demon-hunters I was speaking of earlier. A Shadowhunter's duty is to protect mankind from the demons that inhabit the earth, basically they are pretty bad-ass. Within this world though you also have the "Downworlder's, as you can probably guess are the supernatural beings that essentially come from Hell, or the mixing of certain blood with that of demon blood. For example, warlocks are demon blood mixed with mundane's (human). So that is the type of world that this series takes place in, now let's talk about the main part of the plot of the series.
The series starts with Clockwork Angel. I first read this book probably about a year and a half ago for my book club and I thoroughly enjoyed it. I have a problem though of reading too many books--wait that' s not the problem. My problem is that I have certain books I have to read by specific dates because of book clubs, due dates at the library (yes, I still adhere to them), and my own goal of reading one non-fiction book a month. So books in a series often get pushed back for reading, which is a shame. That is why this year I have deemed 2015 "The Year of Finishing Series". I loved Clockwork Angel so much that I made this my first series I was to finish in 2015. Clockwork Angel starts out with an American girl named Tessa, coming to England to live with her brother after their aunt passed away. Immediately, she gets picked up by the Dark Sisters, who say they are there to pick her up and take her to her brother, but really they hold her captive and torture her, forcing her to "change" (read it to see what I mean). Finally, after weeks of this, she is rescued by a young, handsome Shadownhunter named Will (swoon). He takes her back to the institute, where a few other Shadowhunters and himself live. At the institute, Tessa meets a number of other Shadowhunters, including another handsome young man, Jem, who is Will's best friend. Enter THE LOVE TRIANGLE.
So I read a lot of young adult fiction, and it seems every series out there included a love triangle. It was getting old. But something about this one just worked for me. I think it's because over the course of the whole trilogy, although I did end up being "Team Will", I genuinely loved all of the characters in the triangle. Even Tessa. I cared so much about what happened to them, and whether they lived or died, or found happiness. I don't necessarily think that everyone will agree with me if they read this series, that the love triangle works, but I think you should give this trilogy a shot. Aside from the love triangle, it's full of adventure, interesting Downworlder characters, and mystery. Plus, who doesn't love Victorian London?
Not exactly a detailed review of this series, but I think that's fine because I love it too much to spoil it for anyone. If you like any of the things I mentioned (teen romance, supernatural beings, science fiction, Victorian London), check out Clockwork Angel, Clockwork Prince, and Clockwork Princess.