Chris isn't doing well in school and is going to have to repeat the 9th grade if he fails his next history exam.

Stewie and Peter decide to take Chris on a trip in their time machine and Stewie plots the itinerary.according to the contents of the test.

They first arrive at the White House as Jefferson is announcing the Louisiana Purchase. They then make their way to the home of Ernest Hemingway as Brian bores Hemingway so heavily that he commits suicide. 

They jump around to Brazil before the invention of the soccer ball and Italy before the invention of pasta among other places, before jumping back to the Revolutionary War. 

They then take a couple side trips to Jane Austen to release farts and to famed social scientist Ivan Pavlov for Brian to beat him up.

After all this jumping, they wind up in Great Britain in 1912 and Stewie is mad at Chris for not having learned anything and concludes that Chris is too dumb to pass the test. Chris gets angry and decides to ditch Stewie and Brian and boards the nearest ship. It turns out to be the Titanic. Even worse, Chris has taken the time machine with him.

So now the episode has morphed from a time travel parody to a Titanic parody. Stewie and Brian board the Titanic and hope to get Chris and get off the ship but by the time they get to him and time machine, the Titanic has hit the iceberg. The time travel pad malfunctions as the flood of water rushes into the device. The trio now must get off the ship the conventional way.

They have to dress up as women. Chris pushes someone over the rails and gets them all into a life boat and Stewie and Chris apologize for fighting and hug it out. 

Chris wakes up the next day no smarter than before but he's saved by serendipitous circumstances: The man Chris pushed off the Titanic was the ancestor of the teacher who threatened to flunk Chris.