A 30-year-old man has been arrested after a woman was found lying in a Merseyside street with serious head injuries.
Paramedics and police were called to The Meadow in Woodchurch, Birkenhead, at 2320 BST on Monday.
The woman, 50, is in a critical condition in Arrowe Park Hospital, police said.
Officers want to speak to a group of men, and a man and woman, seen in the area before she was attacked.
Det Insp Mark Tivendale said: "We need to understand how this woman came to be so seriously injured and trace several people we believe were in the area at the time.
"I would urge these people to come forward and tell us what they know.
"We believe there may have been some kind of incident in the street at around 11.20pm, and we also believe there are people in the area who may have information, who could help with our inquiries."