There is definitely heat but a lot of teasing until you reach the second half of the book)
From page one you are plunged into a world of Kin and Mages. Kin are powerful demons who use their magic to transform themselves into beautiful beings that closely resemble humans, while Mages are powerful wizards whose secret long term goal is to rid the world of free Kin.
Grayson Spencer, a human, is forced to choose sides when a evil Mage turns her life upside down. In an attempt to kill him she comes face to face with Durian, an assassin, a Kin. Unable to let Gray complete her mission due to a treaty the warlord he is bound to made with the Mage she wants to kill, Durian works with Gray to find another means for her revenge while trying not to fall in love.
Immortal Assassin is a great start to a new series. It moves quickly and is a refreshing change from the usual paranormal subjects of vampires and shifters. The characters are interesting and easy to follow. I would definitely pick up the next book in the series.