A 24-year-old woman was fatally stabbed in Hayes, west London, early on Sunday, police said.
Officers were called to the property at approximately 07:55 BST. A man in his 20s was found outside with stab injuries and was taken to hospital. A 44-year-old man was arrested on suspicion of murder and possession of a bladed article and was himself taken to hospital with injuries believed to have been sustained from jumping from a window.
The identities of the woman and the second stabbing victim have not yet been released. Police investigations are ongoing.