The book was well paced, and, said in the title, the best book in OOTS so far, with Fading Echoes and Nightwhisper close behind. There was some fillers, although good ones! Vicky Holmes, 1/4 of the Erin Hunters, said that "A dramatic return, even if it's very dramatic, won't fill 300 pages." So obviously they added a filler, because it is over 300 pages. (315 to be exact.) My guess is Sorreltail's kits, but I enjoyed reading about them, so I cannot complain!
Anyways, Hollyleaf IS the Forgotten Warrior, and she first appears towards the middle of the book. Sol also appears, and the prologue is about him making his way towards the clan. He causes more complications during the book, but I will not go too deep in detail.
Hollyleaf was about to admit that she killed Ashfur at a Clan meeting, but Brambleclaw backs her up and says it was an accident, which we all know it was not. So Hollyleaf begins to train the clan in the tunnels, because thanks to Dovewing's powers they know that WindClan is planning an attack (led by Sol).
Yellowfang tells Jayfeather to tell Cinderheart that she was Cinderpelt, and he obeys. Cinderheart then thinks that she has to be a medicine cat, and then when Cherrypaw and Mousewhisker falls ill and Cinderheart rushes in to help, all the clan knows that she was Cinderpelt. I would tell more about how Cinderheart learns, but I don't want to give it away.
Near the end of the book, Dawnpelt accuses Jayfeather for murdered Flametail at a Gathering. The other medicine cats want Jayfeather to step down as medicine cat until StarClan gives them a sign or they find proof, but Jayfeather stubbornly refuses and reveals to everybody that StarClan has sent each medicine cat a sign to go their own ways.
Lionblaze and Cinderheart are still distant from each other, so their relationship gets nowhere, but Lionblaze confesses to Squirrelflight that she was a good mother to him and his littermates, and that she should have had kits with Squirrelflight. He also ends the chapter when Hollyleaf appears with "No! Hollyleaf, I won't let you runaway again!"
The book ends with Dovewing, Ivypool, Hollyleaf, and other ThunderClan warriors leaving the tunnels from the attack from WindClan, whish Dovewing heard and was able to get there before WindClan left the tunnels.
Also, Ivypool kills Antpelt, who died in "Night Whispers" I believe. He, of course, went to the Dark Forest, and to prove Ivypool's loyalty to the Dark Forest she killed Antpelt again. Breezepelt then finds out what she did, and hissed something like "Just because we're both here doesn't mean your my clanmate. You will pay for what you've done!" (Breezepet was Antpelt's clanmate.)
Bumblestripe takes a liking to Dovewing, and Dovewing occasionally thinks of Tigerheart, but declares that "It is too late for us [she and Tigerheat] not to be enemies." When they meet by the border. Dovewing starts to spend time with Bumblestripe, but only after Cinderheart encourages he to.
And that's the main plot! ;)