Sylvain Neuvel's series The Themis Files is a gripping tale where humanity repeatedly guesses wrong, the aliens are tied up in their own soap opera, and giant stompy robots are the least of anyone's problems.
This is one heck of a story. Sleeping Giants, the first novel in this series, starts with the world in geopolitical balance and not much exciting going on. The US government discovers part of an ancient alien artifact made of some super metal. A secret project to locate and reassemble the thing is launched.
The alien artifact turns out to be a giant mech, like Ultraman but weird. The mech inexplicably needs two drivers who are not connected in any special fashion or for any real reason. This is a seriously shitty design flaw, like needing two people to operate the steering and brakes of a car. Regardless, the humans go to monstrous lengths to make it work. They also accidentally kill a bunch of innocent people and some of themselves, sort of.
Curiosity really gets the cat in the one. Over the course of these three books messing around with the mech causes problems interpersonally, locally, internationally and finally intergalactically.
Don't fuck with alien tech. Waking Gods and Only Human are the second and third novels in the series. I burned through all three over the holidays.
The Themis Files by Sylvain Neuvel via Amazon
