An expert in biological warfare, Dr. Hamon Dell, grows a conscience and retires to become a farmer. He begins growing vegetables and sending them as gifts to his former colleagues. After a year, he asks one such colleague, Dr. Curtis Johnson, to pay him a visit. Johnson goes, with the additional assignment to tempt Dell back to his former work if at all possible. Dell refuses:
Scientists, he says, have become the modern mercenaries:
Why the change of heart? It turns out that men have come from the future with warnings of dire consequences if events continue on their current path. In order to prevent the horrors of the future, they are orchestrating a biological war of their own: the vegetables contain a substance that alters the brain to induce empathy in people.
For some men, the brain cannot take the change--the old habits are too ingrained--and it kills them. Dell, it turns out, was such a man. Before dying, he sends Johnson to meet the men from the future, so that he can understand what must be done.
In the end, Johnson resolves to retire, himself, and grow vegetables.