"Anna was beautiful and smart and just the right kind of dangerous to get me killed, which was often what I looked for in a woman, to be entirely honest. The interesting ones are somehow almost always the ones who come with life-threatening risk on the side. It keeps my life exciting, and might also explain why I have trust issues." (Adam the immortal)
Adam has accidentally stumbled upon an important period in history: Vienna in 1814. Mostly, he'd just like to continue to enjoy the local pubs, but that becomes impossible when he meets Anna, an intriguing woman with an unreasonable number of secrets and sharp objects.
Anna is hunting down a man who isn't exactly a man, and if Adam doesn't help her, all of Europe will suffer. If Adam does help, the cost may be his own life. It's not a fantastic set of options. Also, he's probably fallen in love with her, which just complicates everything.