This study analyzes how three groups of market participants - insiders, analysts, and investors - revised their expected returns on New York Real Estate Investment Trusts (REITs) in response to the catastrophic events of September 11, 2001. The attack on the WTC represents a unique experimental setting to evaluate financial markets' reaction to external shocks for several reasons. First, these events, of a totally unanticipated and unprecedented nature, could not have been built into the market's expectations; hence, market participants had to learn something new rather than just recalibrate their expectations on past occurrences. Second, unlike other studies of market reactions, the impact of the terrorist attacks on REIT returns was ambiguous, since it was uncertain if the effect of reduced supply of office space in New York would outweigh the impact of the negative shocks to the local and national economy on its demand. Finally, the period of market closure that followed 9/11 gave these players ample opportunity to reassess their expectations. Our analysis reveals that, on the day when markets reopened, REITs with significant exposure to the New York area outperformed a broad REIT office index by 4.1%. However, we find that, according to several metrics of real market behavior, this anticipated superior performance of New York office properties did not materialize. Consistent with notions of market efficiency, we find that insiders were the first to lower their expectations (99.9% of their trades in REITs with New York exposure were sales in the month following 9/11), followed by analysts (the vast majority of them revised downward their expectations of NY REIT performance in the first weeks of November 2001), and finally market prices adjusted to reflect the underlying real market behavior; indeed, abnormal REIT returns had disappeared by mid November 2001.While the paper is principally about information diffusion, it also presents some very nice data on the resiliency of the New York employment market in the wake of 9/11. New York's refusal to be cowed may be the greatest victory we have had over Al-Qaeda. But that refusal also speaks volumes about why New York became a great city in the first place.