Mr. Lewis tells the policeman that the suitcase in the backseat belongs to Bud. He says that Bud "was visiting here in Flint and (he is) taking him home to Grand Rapids".
The story Mr. Lewis tells is close enough to the truth to allay suspicion. Although Bud had not actually come to visit in Flint, having been trying to get out of the city to find the man he believes is his father in Grand Rapids, the suitcase is indeed his, and Mr. Lewis is indeed taking him "home" to Grand Rapids. The story is plausible enough so that the policeman believes Mr. Lewis without even bothering to look in the suitcase, and even if he had, he would have found only Bud's things in it. Concluding that Mr. Lewis is telling the truth, the policeman sends him on his way.
Ironically, before he goes, the policeman explains that they have "been stopping all cars (they) don't recognize (because) there've been reports that some more of those stinking labor organizers might be sneaking up...from Detroit". Mr. Lewis is very lucky, because in a box which he had instructed Bud to slip underneath his seat when the policeman stopped them are handbills alerting railroad workers to a meeting of the "Grand Rapids Branch of the Brotherhood of Pullman Porters". Mr. Lewis is exactly the type of person whom the police are looking to catch; although he is not a labor organizer, he is active in the movement and is delivering information connected to a planned "sit-down strike" that the authorities are trying to stop (Chapter 12).