Detectives are investigating after the bodies of a four-year-old girl and a man were discovered in a flat.
Police were called to an address in Colville Square, Notting Hill, west London, after concerns were raised about the welfare of its occupants.
They arrived at the scene shortly before 8pm yesterday, and after forcing entry found the bodies of the girl and a man believed to be in his 40s.
Both were pronounced dead at the scene by paramedics.
The deaths are being treated as unexplained and the Metropolitan Police's Homicide and Major Crime Command (HMCC) is investigating.
A woman in her 30s has been arrested in connection with the deaths and is in custody at a central London police station.
No one else is being sought in connection with the deaths and formal identification is yet to take place.
A post-mortem examination will be scheduled in due course and police are in the process of informing next-of-kin.
Police have not released any information about the nature of the injuries.
Anyone with any information can call 101, visit www.crimestoppers-uk.org or contact Crimestoppers anonymously on 0800 555 111.