All Fools Day (1966) Novel.

Summer 1971. A marvellous spell of weather, idyllic in its warmth. But new sun-spots had appeared; and with thier appearance came a significant increase in the suicide rate. The wonderful summer continued for a decade: simultaneously Radiant Suicide reached endemic proportions, the only people to escape its effects being the supposed transnormals, the obesessionals, the eccentrics and the psychopaths. These were to be the only remnants of the ancient 'homo sapiens'...