Why is Volodin arrested in the novel, The First Circle?

The primary character outside Mavrino is Innokenty Volodin, about Nerzhin's age, a diplomat married to a state prosecutor's daughter. Volodin's life is safe and serene as long as he does not deviate from Party policies or ask embarrassing questions. Innokenty's pleasant life is upset when he learns that a prominent Russian doctor will be arrested for a harmless contact with Western physicians. Troubled by the injustice, Innokenty attempts a warning. His phone call is overheard by the secret police who eventually identify and arrest him.