For six months, CERN scientists guarded the best kept secret in science - that they'd seen tiny subatomic particles called neutrinos breaking the universal speed limit. The measurements were at the boundaries of scientific techniques - the discrepancy was just 10s of nanoseconds; parts of their apparatus barely ran at that speed. For six months they checked and then re- checked again every step of their analysis. And still the result held up.

When the results were finally released at the end of September, the headline writers had a field day. Nothing sells copy like proof that Einstein was wrong. But fellow researchers at CERN were less excited. The overwhelming belief was that there still remained some hidden error. And for those who ran the experiment, the dreadful concern that sooner or later that error could turn up, and their triumph might become the stuff of mockery. And the next day the investigations continued.Roland Pease meets the scientists who have staked their reputations on the result, on the critics who think they can spot the mistake, and the theoreticians who think they can explain it all.