Results of cooperative optical observations of EV Lac in September 1991 are presented. During 50 hours of photoelectric monitoring more than 40 flares were detected, including several events of moderate power and one very strong flare with amplitude {DELTA}U=3.7mag and duration of about half hour. Detailed colour analysis of this strong flare indicates that, near the brightness maximum, the flare emission was close to black body radiation with a contribution of radiation from hydrogen plasma, optically thick in the Balmer continuum. The spottedness of the star during this campaign was very even: the detected amplitude of slow brightness variations with the rotational period was {DELTA}V=0.017mag, corresponding to a differential spottedness between the darkest and the brightest stellar hemispheres of only about 3%. The polarization of stellar radiation during the most powerful flare did not exceed 1%.