The two investigators, named Blathers and Duff, enter gruffly and ask to speak with those in charge in the house. They ask whether "a boy" it was who robbed the home; Losborne says that this isn't true, that Giles and Brittles only believes the person they shot was a boy; Blathers and Duff say that they'll check it out for themselves.
Blathers and Duff are named perfectly, as a means of expressing not only their bumbling qualities (a la Bumble), but their total inefficiency and idiocy as regards police investigation. Losborne is able to dispatch them quickly in this chapter.
Losborne is worried that, if Oliver tells the true story of his life to Blathers and Duff, they won't take pity on him the way he and the Maylies have. Rose does not understand how anyone couldn't pity Oliver, and Losborne tells her that, for this, she is a lovely woman; but he insists that Blathers and Duff must be misled into thinking that Oliver was not the person who entered the house the previous night. Otherwise, Oliver could be arrested for vagrancy, as it is illegal for paupers to travel outside of their home district.
Dickens seems to think this "white lie" of Losborne's is OK, considering the circumstances. Losborne is lying to protect a greater good—the health and safety of the young boy placed in his charge. And Blathers and Duff do not appear to have Oliver's best interests at heart—they would be all too happy to arrest a child.
After telling a long, strange, complex story about a robber he once caught named Conkey Chickweed—a story that neither Losborne nor the Maylies can follow—Blathers, with Duff, goes upstairs to talk to Oliver. Losborne and Giles go along as well. Introducing Oliver to the two investigators, Losborne lies and says that Oliver was injured by accident with a spring-gun earlier that day; Giles, at first confused as how to pull off this ruse, eventually agrees with Losborne, and though Blathers and Duff still suspect that a boy, with two larger men, arranged the robbery, they believe Losborne, and do not believe anymore that Oliver is that boy.
Giles seems almost to give up the lie, as he attempts, poorly, to make up a story that gibes with Losborne's. But, luckily, Blathers and Duff are too perplexed by this seeming coincidence to notice, and they eventually allow that it is possible Oliver was shot in an unrelated incident. This is another bit of good fortune in Oliver's favor—his luck is truly turning around.
Before this interview with Oliver, the doctor also pulled apart a section of Giles' gun, rendering it useless; thus Blathers and Duff, on examining the broken gun, saw that, whomever Giles believed to have injured could "not" have been injured at all. This additional lie increases the appearance that Oliver is not the boy Blathers and Duff are looking for; they leave the next morning, and a rumor goes up in London that another two men and boy have been caught, meaning that Oliver is officially free of suspicion (these three others' being caught is simply a coincidence).
An exaggeration of the white lie. Another coincidence also buoys Losborne's lie, and of course Losborne had nothing to do with it. This series of good breaks in the Maylie home seem to indicate that Oliver will be safe there, that his life has changed for the better. Dickens' characters fates seem always to be either on slow upward or slow downward trajectories, with very few interruptions once one is on a given path. Oliver's clearly trends upward from this point on.
Oliver is now safe at the Maylies' home, where he begins to grow stronger, despite his injury. He is looked after by Rose, Rose's aunt, and Dr. Losborne.
This scene recalls the previous scene at Brownlow's, wherein Oliver was cared for by the servants of the house and by Mrs. Bedwin.