Plot
We learn that someone's looking for Tobias, this person who supposedly says she's his long-lost cousin. Tobias isn't so sure of the person's honesty about this fact or it's a trap cooked up by the Yeerks to flush out a member of the Animorphs.
It seems a lawyer has discovered Tobias's father's last will and testament. So, Tobias needs to attend the reading. His "cousin" even offers to go along. But something just doesn't feel quite right. That's when Tobias, the other Animorphs, and Ax decide to do a little checking on this "cousin." And what they discover will change the rest of Tobias's life...
Tobias and his inner demons
Ever since the first book when Tobias was first trapped in his hawk morph, he has struggled with conflicting instincts and emotions as both hawk and human, to survive in the wild with his human instincts in his hawk body.
Tobias in this book, is struggling to survive, to find sustenance as he is battling with a wild hawk for territory and being forced to live off roadkill as he has been dealing with panic attacks while hunting for food and of course dealing with his two conflicting emotions and instincts: hawk's instincts and his human emotions.
He's also finding him forgetting certain details about his old human life, for example: his birthday, what his mother looks like, the more time he's a hawk 24/7 despite regaining his ability to morph again back into his human form thanks to the Ellimist.
Once he finds out about the possibility that he has a long lost cousin despite suspecting it could quite easily be a trap concocted by the Yeerks to capture him and lead to the capture of the others if the Yeerks get smart about the Animorphs' identities.
This cousin could provide Tobias with a real home, a roof over his head, three meals a day, school, and more importantly there's Rachel.
One positive out of all of this and Tobias' continuing struggle to hold onto his humanity and being out of touch with physical characteristics of humanity ultimately saves his life as Visser Three, in Aria morph, observes Tobias, desperate to see whether Tobias reveals any visible reaction to his parental revelation - Elfangor-Sirinial-Shamtul, which makes Ax his biological uncle.
But because Tobias is so completely out of touch being human, as hawks do not have facial emotions, his lack of a reaction convinces Visser Three and DeGroot that Tobias is totally unaware of Elfangor and Andalites.
Tobias feigns that his father was nuts and that the will is useless if he doesn't get any money from it, further convincing both Controllers of his ignorance. "Aria" then fabricates an excuse for no longer being able to adopt Tobias. As Tobias leaves, he overhears DeGroot suggesting that they should infest Tobias anyway, only for the Visser to reply that he is ashamed that Elfangor's son isn't a warrior, and deems Tobias as a waste of a host body.
Overall, this inner turmoil that Tobias has been struggling with since Book One eventually saved his life in this book and by extension his friends, for now, as the Yeerks and including Visser Three, disregarding Tobias and the possibility of being connected to the Animorphs whatsoever, the perfect cover.
By the end of the book, Tobias finds a temporary peace with his dual identities and becomes more confident as he overcomes his panic attacks but also protects the baby bunnies from the rival hawk.
Relationships
Marco and Rachel's relationship is also slightly touched on; when Rachel remarks that in the old days, Marco would find a girl to bother, Marco puts his arm around Rachel's shoulders and states that he now has only one girl to bother. Rachel then laughs and shrugs Marco off playfully, inciting a pang of jealousy in Tobias.
This also brings up Tobias' feelings regarding Rachel and their unconventional relationship which both Rachel and Tobias recognize the limitations of their budding romance. Since their relationship is going through a rough patch considering she's human and he's stuck in hawk morph and they can't do "normal things" that "normal couples" do when in love and Tobias struggles with his identity and his worth to the group and their overall mission against the Yeerks and for someone of Tobias' age to juggle the positives and negatives of his emotional existential crisis, no kid should go through.
With this revelation of the possibility of Tobias having a long lost cousin, Rachel points out there is a chance of Tobias reverting to his human form and having a normal life again but at the cost of his ability to morph and being an essential member of the Animorphs and Rachel being well aware of his struggle to survive in the wild as a hawk and she's not wrong either.
Yeerks .... finally thinking smart for once lol
Chapman has begun looking for Tobias, whom he has realized has missed school for several months and is not living with either of his legal guardians (since both have caught on that Tobias hasn't been living with each legal guardian).
Rachel overhears about what Chapman's up to and discovers that it is because Tobias's father's lawyer, a man named DeGroot, wishes to read Tobias a legal document. To complicate the matter, a woman named Aria, a supposed nature photographer from Africa, has arrived, claiming to be Tobias' cousin and looking to give him a home, of course, alarms go off with the Animorphs as they smell a trap, despite at one point Tobias is juggling with the legitimacy of this claim.
All the while, a young Hok-Bajir, Bek, has gone missing from the sanctuary eventually both the free Hok-Bajir led by the seer Toby and the Animorphs join forces to free Bek and potentially free other Hok-Bajir Controllers from their enslavement which led to both teams learning Aria's true identity as Visser Three in human morph, this blunder alerts Tobias and the Animorphs, which allows Tobias to later foil the Yeerks' plans and saving Animorphs and the free Hok-Bajir from infestation.
As plans go, it's not bad, as the Yeerks are finally dabbling with the possibility that the Animorphs could have human members. If they only knew lol
Conclusion
From this point on, my memories of Tobias continues to struggle with his dual identities and moral dilemma due to this issue throughout the series I can't remember but from this point on Tobias has found emotional peace and confidence that he previously lacked and he has renewed purpose and newfound identity after learning his biological relation to Elfangor and Ax.
Overall, an emotional rollercoaster through Tobias' eyes, of what it means to be human, relationships, survival, and his worth, not just for himself but his contribution to the group, one thing that bothered me even to this book, if the problem is Tobias being stuck in his hawk form and reluctance to be trapped in his human morph and removing his role within the group, couldn't he reacquire the morphing ability from the morphing cube??? It could work as an audience we know so little of the limitations or possibilities of the morphing cube, and don't know if this issue will come back in discussion in later books.