Looks like Ray LaMontagne has a duet with Lisa on the new album, a song called 'O Sleep', from
here:
One notable song is "O Sleep," a duet Hannigan recorded with fellow singer-songwriter and friend Ray Lamontagne.
"I had always wanted to write a proper duet," she said. "Not someone who is just doing backup vocals but people really singing to each other."
She continued, "I've known him for years. And I just think his voice is to die for. It's incredible. Then I wrote the song, I sang the bits and the harmonies and everything, and then I sent it to Ray. And then he said he would love to do the record. We had a day of overdubs in London, and Ray was in London and had a free day. So I asked him to come down and sing. And the moment he sang I knew that it would be beautiful. "