What’s the title? Do you recommend it?
http://www.amazon.com/Gettysburg-Invasion-Allen-C-Guelzo/dp/0307594084
Do NOT get me started on the title. It's inaccurate.
Sterling Price led an invasion of Union states well over a year later, penetrating a great deal farther into MO and KS than Lee did into MD and PA. Wasn't turned decisively back till the Battle of Westport in October of 1864.
To be fair, the CSA claimed MO as one of their states, while they didn't claim MD. But both PA and KS were indisputably Union and free states.
Rant off. :)
To address your actual question, good book. Lots of diagrams.
I have read a number of books about this battle and campaign, but had not previously realized how many times Lee almost broke the Union Army. Or how disorganized the fighting was on both sides. Very little effective coordinating was done by either Lee or Meade. The battle played out as it did mostly due to decisions made at corps and even division level.