There are quite a few examples of secret agent yaois, though many of them are not my kind of thing: heavy into S&M and rape and stuff, whereas I'm a romantic. But, all is not lost. There are some that suit me just fine, including one of Shoowa's works (and I'll be hitting another one not too far in the future), but, in this case it's Koujitsuei no Tobira.
Set in France, it starts out as something that seems pretty domestic, about a man who inherited his apparently estranged brother's adopted son (Kai). But the man (Cys) has a big blank spot in his memory, and can't remember his brother, really, or his life before. But the kid clearly remembers something important.
However, as we add bits and pieces, we begin to see this isn't just a kid, even a weird kid. But he's involved in something big, potentially sinister, certainly not just going to school or a little extra job. At the very least, it's dangerous and something he wants to keep from his "uncle".
The art style is different, a little out of the ordinary, but I learned to appreciate it.
When Kai realizes Cys is catching on to some of it, Kai seduces Cys, seemingly as a distraction but more as a guarantee. Kai's job becomes more hazardous and he struggles to ensure Cys isn't dragged in. When things become a crisis, Cys senses something and uses his own resources to find Kai.
I won't give away any more surprises (there are several more to come) and, ironically, far more of them involve Cys who is not who he thinks he is by any stretch. Some of the key to Cys' past lies in Kai, and some in the people who threaten Kai. It's clever and convoluted.
But, more importantly for someone like me, the characters are believable, charming, thoughtful, passionate, caring and a bit more badass than they look on the surface. There's humor without it being overwhelming. And there's pathos as good people do the wrong thing for fear and confusion--and love. And the motivation why Kai comes into Cys' apparently normal world is a large part of the charm, in the end, of both Cys and Kai. Pretty powerful stuff in the end.
There's intrigue without it taking away from depths of the characters and there are a couple insane people as side characters that have their own twisted charm.