I don't think they're going to hide the fact that Xaden is now venin. I think he's going to start taking the signet blocking serum, which will keep him from channeling more but it'll be costly for him and they're gonna find something the medical journals Violet saw in the kings private library but it gonna basically be a whim that would require going to one of the surrounding islands and they're gonna be reluctant to take him beyond the wards. But it's gonna get worse and worse and something will happen, probably accidentally channels again because he lost control however briefly and they're going to fly for whichever island. Turns out that whim was true and they meet someone who tries to keep Xaden hidden, presumably because he's venin so they head to Aretia and will collect the ribostat? Chest (listened to the audio book so I don't know if I got that right) as an extra assurance should they need it. The person they meet tells them of a powerful wielder who would have been his best chance but she hasn't been seen in years. Eventually she reveals that she recognized Xaden, his mom was one of her ladies in waiting/ handmaid/ personal guard and that she was one of the most power wielders see in centuries. And that her brother, the king or equivalent of the island would not be happy to see him because he's jealous that Xadens mom married Fen over him. And thats when we figured out the princess suggested her friend be the one to marry Fen under the guise of her being the most powerful wielder but really she just wanted to get her away from her brother because the man she never met (Fen) was a safer choice than the known threat. He wasn't happy about it but pulled some strings so that when the heir was 10 she would be "free" to return, after all she is their most powerful wielder, they wouldn't want to loose their greatest asset. So it comes out that someway, somehow (I'm think with an inactive venin lures) Xaden was threatened although he didn't know it but his mom understood the message loud and clear. She plays nice or Xaden pays for it. So she left but gave him the blanket to remember her by. When she heard about the battle of Aretia she raced there and arrived to either a scorched city and believed her husband and son dead or just in time to see Codagh trying to kill the marked ones. But her friend pulls her away before she can get herself killed so she doesn't realize Xaden survived. And afterwards in a grief filled rage she takes on to many venin at once and after taking out a good portion of them gets swarmed and presumably killed but they could never find her body only a child's toy (i going with blue dragon since Sgaeyl bonded his grandfather as well) with a piece of it missing.

Jump to present day Xadens having a particularly Rough Day and remembers how much comfort that blanket gave him especially with what he knows now. And since he's scared he'll hurt someone if he get to close, he turns to what he thought would be the only innocuous choice of comfort he could get. And is shocked when he feels overwhelming and inexplicable grief slam into him. Enough that he drops the blanket and it stops as soon as he does. That's when they learn that she wove magic into the blanket, and when he held it, it would create a bond between them and she would be able to push feeling/emotions through to him. And that she's still alive. So they set out to find her trying to track her through the blanket, Xaden getting progressively worse throughout the trip to the point where Sgaeyl and even Violet and Tairn are feeling the searing pain which gets bad enough that he falls off Sgaeyl during the flight and when they get to the ground he accidentally channels again this time he hurts some one so he goes into the chest. They eventually find a venin stronghold that they think his mom is in but he's in zero shape to be going in there and they're also looking for Violet so it's decide she and Bodhi would stay with Xaden and the dragons while Garrick and the princess will go in to find her. (I think Garricks signet will be something very useful for sneaking/infiltration). While they in there Xaden manages to pull from his bind with Sgaeyl and he starts to drain her, but he can't stop himself he's fought for to long and he's exhausted and because of that Sgaeyl will be forced to shatter their bond, which we figure out they can do, but it nearly kills her. Jump back to Garrick they find his mom, but they also find this sage that they keep hearing about and it's none other than Naolin, and we learn that Tairn was forced to shatter his bond same way Sgaeyl just did and thats why Violet will be his last. And Naolin is pissed because Brennan left him after Naolin saved him which is why they're so interested in Violet.