Domoic acid is a potent neurotoxin produced by marine algae and discovered in 1987 as the cause of amnesic shellfish poisoning. Scientists have made substantial progress in understanding and predicting the conditions that lead to large blooms of the toxin-producing algae (diatoms called Pseudo-nitzschia). But one aspect of these toxic algal blooms, which affect wildlife as well as economically important fisheries, remains a mystery: how do the algae make domoic acid and what triggers its production?