Learn French: Le douanier ne le laisse pas passer le contrôle sans passeport. - The customs officer doesn't let him pass the control without a passport.

When using laisser + infinitive, the object pronoun (representing who is allowed to do the action) goes before the conjugated verb (laisse). Even though he is the one passing, we say ne le laisse pas passer rather than ne laisse pas le passer.

How does the negative ne ... pas wrap around this combination of verbs and pronouns?

The negative halves ne and pas act like a sandwich around the conjugated verb and any object pronouns attached to it. Here, the pronoun le and conjugated verb laisse form a single unit, so the negative wraps around them both to make ne le laisse pas. The infinitive passer stays outside the sandwich.

Why is there no word for 'a' in sans passeport?

After the preposition sans (without), French almost always drops the indefinite article (un, une, or des) when talking about a general item that a person would typically just have one of.

Could I say passer au contrôle instead of passer le contrôle?