Ray Monk in the New York Review of Books:
Thus, in the New Year of 1929, was Ludwig Wittgenstein’s return to Cambridge announced by John Maynard Keynes in a letter to his wife, Lydia Lopokova. Wittgenstein had previously been at Cambridge before World War I as a student of Bertrand Russell, but had acquired his godlike status through the publication after the war of his first and only book, Tractatus Logico-Philosophicus, which was very quickly recognized as a work of genius by philosophers in both Cambridge and his home city of Vienna. Wittgenstein himself was initially convinced that it provided definitive solutions to all the problems of philosophy, and accordingly gave up philosophy in favor of schoolteaching. In 1929, however, he returned to Cambridge to think again about philosophical problems, having become convinced that his book did not, in fact, solve them once and for all.
What drew him back to Cambridge was not the prospect of working again with Russell, who by this time (having been stripped of his fellowship at Trinity College, Cambridge, because of his opposition to World War I) was a freelance journalist, a political activist, and only intermittently a philosopher. Rather, it was the opportunity of working with Frank Ramsey, the man who had persuaded him of the flaws in the Tractatus. Most significantly, Ramsey had shown that the account Wittgenstein gives of the nature of logic in the Tractatus could not be entirely correct.
More here.