This form is composed of two elements: the appropriate form of the verb to be + to (am to, are to, is to), and the infinitive of the main verb without 'to'..
|Subject||to be to||infinitive without to|
|You||are not (aren't) to||travel|
This form refers to an obligation to do something at a time later than now. It is similar to 'must', but there is a suggestion that something has been arranged or organised for us. It is not normally used in spoken English, but might be found in spy stories, e.g.
- "You are to leave this room at once, and you are to travel by train to London. In London you are to pick up your ticket from Mr Smith, and youare to fly to your destination alone. When you arrive, you are to meet our agent, Mr X, who will give you further information. You are to destroythis message now."