Tobias and the angel start out on their journey. The first night, they take lodgings near the Tigris river. Since indoor plumbing hasn't been invented yet, Tobias goes down to the river for a bath. While he's washing himself, a fish leaps out of the water and tries to eat him. Raphael, mindful of the tip Tobit promised him if he returns Tobias in one piece, instructs him to get hold of the fish, remove its heart, liver and gallbladder and put them somewhere safe. Then they have a nice fish fry for dinner.
The next day, they head for a place called Ecbatane. To make conversation, Tobias asks what the angel intends to do with the fish organs. Raphael explains that if they smoke the heart and liver near someone who is possessed by a devil, it will drive the evil spirit away. The gall cures white eyes. Perfectly good alternatives to psychotropic drugs and cataract surgery, which is why you see biblical literalists using them all the time.
At some later point, they arrive in Rages and Raphael drops the bombshell on Tobias that they're going to his cousin Raguel's house, where Tobias is going to exercise his right to claim her as his wife. Sure, Raphael tries to spin it as she's pretty and smart and she can't marry anyone else because according to Mosaic law, her father has to marry her to Tobias because he doesn't have any sons and so Tobias is now his heir, but it still earns this reaction from Alison Brie:
Tobias, demonstrating that he's possibly not the idiot his parents think he is, asks about Sara's other seven husbands who all died in bed with her. He doesn't want to be Henry the Eighth. Raphael reminds him of how he promised his father he'd marry one of his kinswomen and promises to take care of the evil spirit. Oh, also this is where the fish stuff will come in handy: he's supposed to smoke the heart and liver of the fish and lie down on a bed of ashes of perfume (v. 16). The devil will smell all of this and run away, as would any sane bride. But then Sara has already been married to seven guys who all died when they tried to have sex with her, which does not speak well of her mental state. Anyway, as further assurance against premature death, but not premature ejaculation, Tobias and Sara are also supposed to pray to god when they first go into the honeymoon suite, following which Sara will be able to go home with him and start on the continual pregnancies. This causes Tobias to fall in love.