How is it that Frank learns the reason why in Chapter 26 the Defense Ministry not only releases him from responsibility for Volodya, but also encourages him to depart Russia at his earliest opportunity?

Frank learns why the Security Police in the Defense Ministry release him from responsibility for Volodya and encourage him to depart Russia through his piecing facts together. Frank initially receives a letter from the Defense Ministry advising he is no longer accountable for Volodya and urging him to leave the country soon. Then, in the following chapter, in talking with Dolly, Frank learns that Lisa places the children on the train so she can escape to Berlin. He now understands why the Security Police favor his leaving Russia quickly--it turns out that Frank has had a dangerous employee, supposedly looking after his children.