More like 3.5 stars, close to 4. The story was fascinating, with good characters, and just had a few silly elements that disrupted it for me.
The main one was the whole idea of the elaborate wax masks that somehow let the assassins pretend to be other - well-known!! - people for MONTHS. It's one thing to slip in and out of the shadows for brief glimpses, but Xiahou Lian made a mask of a eunuch he'd never even seen, based on a drawing Xie Jinglan made for him, and lived as that person for a considerably long time, with no one suspecting a thing? Even when the guy he was pretending to be had been explicitly described as being very overweight, and no one ever commented on the fact that the "smallpox" he'd contracted had made him shrink from like an XXL to a Medium.
Another plot point that made very little sense was Xiahou Lian being installed in Xie Jinglan's household to begin with. At 12 years old, he talks big (to himself) about being an assassin, just waiting there for his mission to be assigned to him, but it turns out that he was not only not an official assassin by any means, the only thing they ever had him do was go into Xie Jinglan's father's office to read some letters. One time.
Which wasn't even necessary, because the same day he did that, another seasoned assassin (the expert at the appearance-masking skills) entered the same office on his own infiltration mission.
So why was Xiahou Lian there, other than for story-related reasons? It's a kind of gaping hole that I'm willing to ignore because I obviously enjoyed the relationship build with Xie Jinglan very much, but it does drop the overall rating down a bit.
Another point of confusion: the abbott, the leader of the assassins, is described as both an extremely old man on the edge of death, and also an assassin of such immense skill with the blade, he can even defeat Xiahou Lian's terrifyingly powerful mother. I assume he'll actually be a character we'll see more of in future volumes, to better understand what he's actually like, but I couldn't reconcile the different portraits of what he was supposed to be.
The heart of this story, though, is the relationship between Xiahou Lian and the neglected third son of the Xie household, who is the only one to escape the head eunuch's paid-for slaughter. Xie Jinglan is fascinating because he has a cruel, ruthless core that everyone except Xiahou Lian seems to recognize. He is far more of an assassin than good-hearted, kind, friendly Xiahou Lian could ever be...and in fact, by the tender age of 14, he's killed more people. Meanwhile, Xiahou Lian is mostly just being sent off on information-gathering missions because he hates killing people so much he fumbles every job.
I found their relationship really interesting. Right now, it's very unbalanced: Xiahou Lian keeps sacrificing for Xie Jinglan, while considering him a friend and a brother. Xie Jinglan is very clearly the only one who is developing romantic feelings at this point - or at least, in a way where he's actually recognizing that he sees Xiahou Lian in a pretty non-platonic light. Xiahou Lian is devoted to him, but Xie Jinglan is desperate for him: he has a very small, selfish heart with very little room in it, and right now Xiahou Lian is taking up the entirety of it.
There's a two year timeskip before they meet again in the imperial palace, and I'm assuming there will be several more years passing before the next volume begins, since this one ends with them parting ways again. Definitely looking forward to seeing more of them as adults.
My biggest surprise was how attached I was to the secondary, straight couple: the shy and honorable imperial soldier and the pretty, outspoken doctor's daughter who promised to follow him into exile if he didn't come back for her. Maybe the rating is reduced a little too because I ended up being more interested in following their story...
But this was an intriguing start to a series, and it's always refreshing to read one that's grounded more in real-world intrigue and sword skills that are developed from boots-on-the-ground hard work. Except for the silly reality-bending wax masks.