A suspected killer was tackled by London Underground workers as he wandered nearby carrying a bloody weapon.
The man, believed to be aged in his 20s, was seen wandering close to the car park at Finchley Central Station, in north London, at about 2.30am.
Tube workers confronted the man, who had blood on his clothes and was drunk, and held him until police arrived.
The man was taken to a north-west London police station for questioning before officers attended a flat in nearby Station Road.
They discovered the body of a woman. An ambulance was called and she was pronounced dead shortly after 3am.
She is thought to be the arrested man's mother and is aged in her 50s. The man is thought to be of African origin.
A Metropolitan Police spokeswoman said: "We await to inform next of kin and for formal identification to take place. A post-mortem examination will be scheduled in due course."
Cordons are in place in Station Road, a busy street of Victorian terraces, many of which have been subdivided into flats.