The story so far: Takasu Ryuuji and Aisaka Taiga are the most feared kids in their high school. In Taiga's case this is a well-earned rep, but Ryuuji is a good kid who had the misfortune to inherit his yakuza father's mean looks. Ryuuji and Taiga are both in love with the other's best friend (Kitamura Yuusaku and Kushieda Minori) and agree to help each other. Along the way Ryuuji ends up taking care of Taiga, who has been abandoned by her parents in a luxury apartment next door to the Takasu's tenement. By the end of the first book, Taiga was practically living in the Takasu place, only returning home for bed (when she didn't fall asleep in front of the TV). This causes problems when other students notice the situation and conclude Taiga and Ryuuji are a couple. Which, you know, kinda puts a damper on their romantic plans. Nonetheless, they'd developed enough of a codependent relationship by that point that they couldn't quit each other, so they had to settle for convincing Kitamura and Minori that nothing's going on.
Book 1 ended with the establishment of a status quo, which is death for romantic stories, so Book 2 begins with a complication. Raymond Chandler once said that if you can't think of what happens next, have a man come through the door brandishing a gun. The rom-com version is to have a beautiful woman come through the door in a sexy dress. And so the book opens with Ryuuji and Taiga having lunch at a restaurant when Taiga notices a beautiful woman enter. And not any beautiful woman -- this is Kawashima Ami, the famous fashion model. And she's accompanied by Kitamura! They join Taiga and Ryuuji, and Kitamura explains that Ami's an old friend of his family who's in town visiting.
Ami seems like a sweet girl if a bit of an airhead, but when Kitamura and Ryuuji go to the bathroom, she reveals her true, bitchy self to Taiga. They get into an argument that ends with Taiga slapping "the stupid chihuahua" ("Sorry, you had a mosquito on your cheek. Oh, you have a fly on the other one.") But the guys didn't really go to the bathroom -- Kitamura knows about Ami's mask, and he wants Ryuuji to see it as well.
We find out why the next day in class when the teacher introduces a new student, none other than Kawashima Ami. The situation quickly deteriorates as Ami decides to crush Taiga -- and unfortunately for Ryuuji, she picks him as the tool for doing it.
Ami makes a great addition to the cast. Takemiya does a wonderful job portraying her dual personalities -- and making her inner bitch more likable than the "stupid chihuahua" facade. Sure, she's mean, petty and mercenary, but no worse than Taiga. It's her "Ami-chan is so cute," act that makes her such a perturbing character. There's a scene where Ryuuji and Ami get caught in the rain and her mask slips, which is the first time they're able to have a real conversation instead of Ami manipulating him with smiles and gentle caresses, and for a moment, before she falls back into her act, it seems they could be friends.
As a foil for Taiga, Ami is perfect. Anyone else, Taiga could simply intimidate, but if she tries that on Ami, the other girls in class, who absolutely adore Ami-chan, would turn on her. All Taiga can do is wait for Ami to make a mistake and pounce, such as a moment when Ami tells the class that she's just naturally thin and doesn't need to diet, which of course pisses the hell out of all the girls who eat salads at lunch and spend hours at the gym.
The first book was essentially a prologue that established the set-up for the series. This volume is where the real story kicks in. While it contains a plot in its own right, with a beginning, middle and end, it also establishes an ongoing conflict between Ami and Taiga, of which this is merely the first installment.
(NOTE: Don't expect to find this book on Amazon or in your local bookshop. From what I've read, there's no interest from American publishers in the series (most of the companies that publish Japanese fiction focus on sci-fi and fantasy). Even the anime adaptation only got a half-hearted release -- the distributor didn't even spend money on a dub track, a sure sign that they weren't expecting it to be a mass success -- so it's unlikely that an official release will happen in the foreseeable future. However, all ten books have been translated by fans, and you can easily find them by googling "Toradora epub".)