Laura Marling, Hyde Park, London

"Here's a very depressing song to start proceedings," Laura Marling said, barely audibly, kicking off her Serpentine Sessions set.

The diminutive 20-year-old, high priestess of a new brand of pop-folk, then belted out the optimistically titled, but miserable, "Hope in the Air", the best track on her new album, I Speak Because I Can. The blue-eyed poster girl for a "scene" occupied by artists including Noah and the Whale, Mumford & Sons and Johnny Flynn, whose voice pitches somewhere between Joni Mitchell's and Kate Rusby's, effortlessly, if nervously, mesmerised her audience.

Songs of suicide and unhappy love affairs proliferated. But the 3,000-strong crowd, sticky and swaying in a red plastic big top, excitedly welcomed "Ghosts" from her first album, a moribund ditty about the ghosts of failed relationships. Gasps of "I love this one!" rippled through the audience, a man screamed out "beautiful!" and the masses sang along: "The ghosts, the ghosts, the ghosts that broke my heart." Another new song "Blackberry Stone" kept momentum, then, with cracked emotion, "My Manic and I" raised hairs on arms. Marling apologised between songs for being "unable to get away with stage banter."

Seven tracks in and the band left the stage. Alone, Marling – shrugging in her grey cardigan and black jeans – filled the dark stage with her piercing melodies. An eerie rendition of "Goodbye England (Covered in Snow)" was greeted enthusiastically, despite its incongruity on this sweltering evening. Next, her suggestion that the crowd whistle the violin solo from "Night Terror" was keenly, if badly, acquiesced to. Her singing was faultless.

"I think we're having a good time," she said sadly, and not totally convincingly. She finished with "I Speak Because I Can", about a scorned wife, filled with bitterness and a touch too much vibrato. A satisfied, but somewhat dejected crowd filed out.