Almost five centuries after the first Foundation was established the ambitious councilman Golan Trevize is convinced that, despite the common belief, the mysterious Second Foundation still exists.  Even more: they control the First Foundation far more fundamentally than the First Foundation's Mayor is willing to accept.  Trevize, eager as he is, brings his message at the wrong time, in the wrong place, and in the wrong way.  To his bitter surprise he learns Mayor Harla Branno knew of his ideas, and she now sees the right circumstances to send him away on a mission.  Officially he is sent into exile, he will become the guide of professor Janov Pelorat on his search for the mythical cradle of mankind: the planet Earth.  But secretly Mayor Branno hopes that Trevize will act as a lightning conductor that will attract the attention of the Second Foundation...

That Second Foundation is quite pleased with itself, as it managed to overcome the ripples the Mule has caused in the normal flow of the Hari Seldon Plan.  For almost two centuries now that Plan is quite perfectly on track.  Too perfectly, according to the ambitious Speaker Stor Gendibal.  He gives proof that shows something or someone managed to tamper with the Seldon Plan, but oddly enough for the better.  He suspects the existence of what he defines as "anti-Mules", and he believes Golan Trevize is some kind of a key element in whatever it is they are planning to do.

Gendibal is manoeuvred towards the finale of this all, accompanied by the Hamish woman Suri Nova, used by him as a detector for mental attacks.  With a stopover in Sayshell Trevize and Pelorat are travelling towards the same location: a mysterious world that managed to stay hidden from just about everyone and everything, so far.  Now they feel ready to come out, and act as a third player in the game between both Foundations...

This is the 4th book in the Foundation series, but the first real novel.  The original trilogy was a collection of shorts stories and novellas.  This means that Asimov now has the time to develop his characters far deeper than was possible so far.  Of course the pace is influenced by this, and that may disappoint many fans of the series.  But on the other hand it means the few characters there are come to life much more than in the previous series of stories.

To be really honest, it's not quite the best of the series.  Not that much happens, but still many elements are quite interesting.  Finally we learn some more about that mysterious Second Foundation, finally we understand them and their relationship with the rest of the planet they're on a bit better.  And the ending is, unspectacular as it is, a surprise that leaves enough open doors for future novels, novels for which Foundation's Edge provides some needed cornerstones.