At the start of The Fellowship of the Ring, Frodo Baggins receives the Ring from Bilbo, and continues to live happily in the Shire for seventeen years without much trouble. But even at this point, we know that Frodo has been marked for something different from an ordinary Shire life. The whole neighborhood thinks Frodo is a weirdo: he doesn't find much understanding in the Shire, so it's clear from the beginning that his destiny lies in the larger world – just like Bilbo's did in The Hobbit.
Something terrible is on the horizon: Frodo's Ring, which Bilbo found in the Misty Mountains during his adventures in The Hobbit, actually holds part of the worst evil currently living in Middle-earth, Sauron. To make matters even more dire, big-mouth Gollum spilled the beans of the Ring's whereabouts, and Sauron has sent servants to claim the Ring from the Shire. Frodo has to get out of there as soon as possible.
In Chapter 6, Frodo leaves the Shire with his companions Sam, Merry, and Pippin. But their decisions are mostly disastrous, and we start to wonder if Frodo really is the right Hobbit to be Ring-bearer. Many complications arise – from a Hobbit-eating evil willow tree to the evil Ringwraiths who almost kill Frodo – and Frodo has to try to protect his whole Company from disaster. How are these inexperienced Hobbits going finish their journey in one piece, with the Ring safe?
The thing is, Frodo has shown that he is quite resistant to the temptations of the Ring. The problem is, the other members of Frodo's new Fellowship do have glorious ambitions, particularly Boromir, the man from Gondor. From the moment Boromir suggests using the Ring to defeat Sauron in the Council of Elrond, we have suspected that he is going to do something stupid. By Book 2, Chapter 10, that stupidity comes to pass: Boromir tries to steal the Ring from Frodo. He basically goes nuts and tries to attack Frodo – talk about a climax.
After the attack, Boromir returns to the company And admits that Frodo vanished after they spoke about Minas Tirith. Everyone panics and they all dash off to find their leader. Will they find him? Will the Company continue on together or be torn apart? Did Frodo really leave? So many questions, so much suspense.
With Boromir's betrayal, Frodo finally decides that he must leave the Fellowship, for the good of his friends as well as for the quest. Sam, the loyal friend he is, finds Frodo and insists on accompanying him on his journey to Mordor. With fewer people – especially fewer non-Hobbits – the Ring quest seems more hopeful than it did with Boromir skulking around.
The story has now split into two pieces. Frodo has to keep struggling with the Ring, since he is the Ring-bearer. And the other members of the Fellowship (minus Sam, since he, of course, follows Frodo) have to fight Sauron without worrying about the Ring's temptations. There is too much struggle in these two battles for the Fellowship to tackle both problems at once. But while the breaking of the Fellowship is a conclusive moment for Frodo's plot arc from uncertain and inexperienced Shire resident to daring adventurer, there are still a lot of questions left unanswered. To answer at least some of these questions, next up, we have The Two Towers.