What transpires after Frank receives a telephone call from the Security Police on Palm Sunday?

On Palm Sunday Frank gets a telephone call from the Security Police who advise they are detaining one Vladimir Semyonich Grigoriev, a student who has confessed to breaking into Reid Press. They ask Frank to come to their office to identify him. But while Frank is there, they ask him to confirm their information about his household staff. They further indicate that they are aware Frank has been taking steps to sell Reid Press, and that he might have plans to leave Russia. Frank does not contest anything they say, but advises that he does not intend to depart Russia presently. They advise that all of his exit permits might be made legally invalid. They also advise Frank that he is now fully responsible for Grigoriev and, as long as he is a student at the university, Frank is not allowed to depart Moscow.