I think out of the three this was my least favorite of the infernal devices series. I like action more than romance books and this one had a lot of Tessa swooning over both Jem and Will, Harry and Charlotte, Sophie and Gideon, Cecily and Gabriel. Very mushy gushy romantic, so if you like that kind of thing you will like this book a lot I think.
What I really like is how the two series (Internal Devices and Mortal Instruments) Interweave with each other. Things that you have read in the present with mortal instruments are more chiseled out and understood more in Internal Devices. Like how Church came to be in the New York institute. And, how the Herondales got the star like birthmark on their shoulders. It is like you are reading about the great great grandparents of the kids of the Mortal Instrument series looking into the past of the families and finding out more about stuff that you were familiar with in the present.
Clockwork Princess starts out with Tessa getting ready to get married to Jem. Getting her dress fitted, but then things start to come apart when Gideon and Gabriels father is found to be a worm. And one thing leads to another with there search to find The Magister. The book is sad, people die but then people also fall in love in this book as well. This book does have it all, romance (alot), action(a little), death, destruction, plots revealed and everything ties up nicely at the end.
But all in all it felt the same as the two books before. I guess I am not a love triangle type of gal.