This is clearly on the one hand an immensely amusing part of the novel, as Huck is reunited with Tom, and immediately takes on the role of sidekick to him. Huck devises a simple plan to free Jim, but Tom, typically, dreams up an incredibly complex plan which wins the day. Note how Tom complains about Huck's simple (but far more effective and logical) plan:
"Work? Why, cert'nly it would work, like rats a-fighting. But it's too blame' simple' there ain't nothing to it. What's the good of a plan that ain't no more trouble than that? It's as mild as goose-milk. Why, Huck, it wouldn't make no more talk than breaking into a soap factory."
I think that Twain includes Tom's incredibly complex and ludicrous rescue plan to show us about Tom's character. Throughout the attempt to set Jim free, Tom complicates simple matters. When events do not occur exactly as Tom envisions them, he modifies his elaborate plans. Yet all the time he tries to mimic the plots of romantic novels. What is interesting of course is that Huck, who has shown himself to be incredibly self-reliant and versatile in the middle chapters, now willingly takes second fiddle to Tom.
What also adds a somewhat darker note to these chapters, and indeed to Tom's character, is the fact that later we find out that Tom knew that Jim was a free man all along, and thus shows how he is playing with the fate of a black man because of racial inequality.