Murder of a Suicide

When Toby Dyke and his companion George get caught in torrential rain one night they are surprised to find that they are not the only ones out in such a fierce storm: Edgar Prees aging botanist of prestige and reputation is attempting to commit suicide by jumping off a cliff top. The two men drive Edgar home collapsed and shaken. When he is then found the following morning shot dead with his own revolver it seems that his attempt at suicide has succeeded - but is the case really as clear-cut as it appears?