Some time in the future, an advanced civilization has found a marker left by precursors, pointing at habitable worlds. The first intelligent life they find by following the marker is humans. They form some sort of union committed to peaceful exploration of the cosmos, and find a marker near or on Earth, left by the same precursor.
The story is about a team of explorers who followed these markers and found a space-faring civilization that was less advanced, so the explorers try to remain covert to avoid cultural contamination (sort of like the Prime Directive in Star Trek). Something goes wrong, and the main characters are stuck on a planet, and have to avoid detection by the locals.
While that's happening, the federation moves to effect a rescue of the stranded characters.
I read this in or before 2012. I know for sure it's not a Star Trek novel. It was similar to Enchantress from the Stars, but with no psionics.