Atlantis Betrayed by Alyssa Day

The narrative chronicles the fraught partnership between Christophe, an ancient Atlantean warrior, and Lady Fiona Campbell, a Scottish aristocrat who secretly works as the benevolent thief known as the Scarlet Ninja. They are united in a high-stakes hunt for two magical artifacts, the sword Vanquish and the powerful gem Siren, which is essential for the hidden city of Atlantis to finally rise from the ocean floor. Their mission is complicated by escalating attacks from ruthless vampires and interference from the royal Unseelie Fae, particularly Prince Gideon na Feransel, who desires Fiona as his unwilling bride. As they navigate London's supernatural underworld and form a deep, magically charged connection, Fiona is introduced to the world of Atlantean royalty and aids in the ensuing conflict against the supernatural forces vying for global control. Ultimately, their alliance, confirmed by an ancient soul-meld, leads them into the Fae realm to rescue her captured brother and defeat the hostile prince.