Baby, It's Cold in Space by Margo Bond Collins

And now he wants her to pretend to be his date at several events. To make matters worse, she’s sent to New London-the most backwards, useless planet in the Coalition, as far as Gabi can tell-to play bodyguard to one of its silly nobles in the midst of its most ridiculous holiday season. Instead, she got posted to the Achilles, a battleship past its prime on a milk-run assignment in the dullest end of the galaxy. When Private Gabi Esser joined the Galactic Coalition Fleet Marines, she had dreams of seeing the universe. When the Coalition sends him a beautiful Marine to act as his personal bodyguard during negotiations, he sees a chance to buy some time, if only she’ll agree to play along. Unfortunately, keeping his new post as Ambassador to the Coalition depends on remaining a Peer, and to keep his dukedom, he has to at least look like he’s on the marriage market.

When her arrival in modern-day Greece leads her to an American detective, Skyla realizes that the magical problem she's been sent to research is bigger than she anticipated-and that one human's kisses might be more dangerous to her, and her world, than she ever could have imagined.Edward Sullivan, Duke of New Wiltshire, is far too busy trying to drag New London into the twenty-eighth century to spend time finding a wife. But her studies are interrupted when she is called upon by Poseidon himself to investigate rumors that the world above is being polluted by the magic of creatures from another realm-and worse, that the ocean kingdom of the mer-people might be next. Ever since, she has lived in the underwater ruins of Atlantis, studying with the priestesses of the goddess Amphitrite, refining her mermaid powers and ignoring her human half. Unless his kiss kills her first.It's been almost two thousand years since the mer-shifter Skyla walked the streets of Athens-not since her heart was broken by a human man and she exchanged the land and sky for the ocean depths. But her studies are interrupted when she is called upon by Poseidon himself to.

Baby, It's Cold in Space by Margo Bond Collins