For a MG book, I'm surprisingly intimidated by the prospect of trying to give a synopsis. That's probably a clue about the book. Brangwain Spurge is an elfin historian of moderate renown -- when (as far as he knows) an ancient goblin relic is found in his land, he's dispatched to present it to the goblin's king. No elf has survived being in -- much lest returning from -- goblin territories in more than a century, but the conventional wisdom is that a historian should be safe -- even if he is also spying.
The goblins and elves have spent centuries fighting each other, and are in a rare season without warfare -- and no one expects it to last for long. Each side distrusts the other in ways that make relations between the USA and USSR in the 1960's seem warm and cordial. So this mission of Brangwain's is an unexpected and welcome overture of peace. Or so many people think.
Brangwain's host is a goblin names Werfel -- who's also a historian. Werfel is a very odd, but seemingly pleasant, person living in the midst of pretty odd, and apparently pleasant, people. Every goblin he meets goes out of their way to welcome Brangwain and try to make him feel comfortable, while celebrating elfin culture. Brangwain's a nervous guy, who has spent most of his life (going back to childhood) being insulted, bullied and overlooked -- he doesn't really see the efforts of the goblins for what it is. Besides, he's too busy trying not to get caught while spying on his hosts.
Now, how does this elf -- who most people expect is on a suicide mission -- get his information back to the elves? I'm glad you asked -- this is an ingenious move by Anderson and Yelchin -- while alone and resting, Brangwain uses elfin magic and imagines what he's seen which is transmitted to a device in the office of his king's military intelligence, that takes these transmissions and "prints" them out. These would be the illustrations that make up a significant portion of this book.
Ultimately, things go awry and Brangwain and Werfel are on the run together, trying to survive and hopefully keep the peaceful overtures alive. A friendship will rise between the two as they depend on each other and realize how much they have in common.
There's some great commentary on the power of perspective when it comes to history. Werfel and Brangwain differ greatly in their understandings of the same event/person, wholly dependent on their backgrounds. It's all about who writes the history -- even if it's an obscure scholar -- when it comes to establishing "fact."
A little bit more about the art. First, it's just great. This isn't a book directed at the picture book crowd, but the art might as well be for people who can't read the text -- it's as much of the story telling as the text. Yelchin actually saves them a couple hundred pages telling the more dramatic portions of the story in his pictures. Interestingly enough, the events described in the narration and the events depicted in the art/Brangwain's reports differ significantly, and part of the fun of the book is comparing them. Yelchin's art reminds me of Jules Feiffer’s from The Phantom Tollbooth, which is possibly the biggest selling point for me. Well, except the picture of a spider-creature that makes Shelob and Aragog look tame.
It's a fun story, a little wry, and it will appeal to grade schoolers who have an off-kilter sense of humor. I really enjoyed reading it and recommend it for middle graders and their parents/older siblings alike.