So far I've read Asimov's four Robot novels and all three Empire novels. I haven't read the Foundation series yet. Pebble in the Sky is the last of the Empire trilogy. It's a good read but I didn't enjoy it as much as the other Empire books or the Robot series. I feel that science fiction is most enjoyable when it's somewhat believable, but Asimov nonchalantly combines three far-fetched concepts in this work: time travel, telepathy/ mind control, and a weapon of extreme mass destruction. It's a bit too much!
A man named Joseph Schwartz is for no reason warped in time to the far future when the Trantorian Empire (introduced in The Currents of Space) has conquered and brought general peace to the entire Milky Way galaxy. The novel takes place wholly on Earth but the Earth of the future is a shattered and largely radioactive planet that bears little resemblance to what it is today. There is no space travel in this book.
After the random time travel event, Schwartz proceeds to acquire superhuman powers and uncovers a conspiracy that threatens the Empire, helped by a couple people who really just end up being the supporting cast for Schwartz's show. The viewpoint of this book is interesting: the "good guys" are the vast and powerful galactic Empire and the "bad guys" are some militant activists on Earth!
Overall, this book was a letdown after The Currents of Space, my favorite of the seven Asimov novels I've read so far. Still, it gives you an interesting perspective on the Empire at the peak of its power. From what I've heard, the Foundation series is where the Empire begins to crumble. So read the Empire series if you want to get a better idea of what life in the early Trantorian regime was like!