Immortality: A love story - Dana Schwartz

Hazel Sinnett is alone. She's half-convinced the events of the year before - the immortality, Beecham's vial - were a figment of her imagination. She doesn't even know if Jack is alive or dead. All she can really do is run her free clinic, helping people and maintaining Hawthornden Castle as it starts to decay around her.
When saving a life leads to her arrest, Hazel seems doomed to rot in prison until a message intervenes: Hazel has been specifically requested to be the personal physician of Princess Charlotte, the sickly daughter of King George IV. Soon Hazel is dragged into the glamour and romance of a court where everyone has something to hide, especially the ladies of the princess's close circle, who never seem to stay hurt for long . . .
Meanwhile, Jack Currer has been trying to find a way to die. He's been traveling across the Atlantic, hoarding any information that could cure his immortality and let him spend a normal life with Hazel. When he hears that Beecham has died, he immediately goes to London to find out how he achieved it - and reunites with Hazel once again.
As their search for the immortality cure entangles them more and more with the British court, Hazel and Jack realize that a life together is not the only thing at stake. Malicious forces are at work in the monarchy, and they are very interested in living forever . . .