My wife and I watched this at home on DVD from our public library. We both found it a very worthwhile movie, a bit underrated in my opinion.
It is set and filmed mostly in England, including London, with brief scenes in New York. Chris O'Dowd is Duncan Thomson who in almost all of his spare time obsesses over an American singer/songwriter who was popular 25 years earlier and has essentially disappeared. He and others frequently hold podcast discussions and speculate on where the musician might be.
He has a live-in girlfriend, Rose Byrne as Annie Platt. She feels Duncan neglects their relationship, rightly so, and on a whim posts a contrarian, somewhat negative comment to Duncan's website. Then she gets a surprise response, supportive of her views, from none other than the long-missing musician.
Ethan Hawke is that musician, Tucker Crowe. Basically he thinks all the adoration he receives is silly, himself having low regard for his early work. As fate would have it his British daughter is having a baby requiring him to travel to London where he and Annie will have a chance to meet.
The story gets a bit complicated but in a good, interesting way. Annie is approaching 40, she has no children, she is afraid life is passing her by. Tucker feels he has frittered his life away and approaching 50 wants to have another chance. Good story, authentic acting, a meaningful movie with lots of funny moments sprinkled in.