There is a kingdom and in the kingdom when you drink a poison the only way to cure yourself is to drink a stronger poison to neutralize it. The King wants to make the strongest poison possible in order to make sure he can neutralize any other poison he may be given. To do this he enlists the two best chemists of the land: Tom and Bob.
The king is going to have them both create a poison as strong as they can then have them drink the other person's poison then their own. Whoever dies created the weaker poison. Tom knows that Bob is much better at making poisons and he is sure to make a stronger poison. Knowing this, Tom makes a plan that ensures he lives and Bob dies.
The day of the contest arrives and Bob realizes that Tom must have known he had no chance against his prowess as a poison maker. So Bob thinks quickly and creates a new plan that ensures that once again he will live and Tom will die.
In the end Bob lives, Tom dies, and the King doesn't get what he wants.