Six people, including three children, have escaped without injury after a petrol bomb was thrown into their home.
The device set alight part of the house in Antill Terrace, Stepney, east London, early on Thursday.
A couple and their three young boys - one of whom is a month old - were asleep at the time, along with a male relative who was staying with them.
Police think the attack may be related to a case of road-rage involving a man who had visited the house earlier.
The arson attack happened at about 0250 BST.
Three hours earlier, a man had left the house after a birthday party.
When the man got on his bicycle outside the property, he was knocked to the ground by a black VW Golf, leaving him with a grazed leg.
The car stopped and a row broke out between the cyclist and the driver with the motorist suffering a cut to his head, police said.
Officers were called but no arrests were made as the situation had calmed down.
A Met spokesman said "neither party wanted to involve the police".
However, it was later reported that the driver allegedly threatened to shoot the cyclist.
At about 0230 BST, a bullet was fired through the living room window of a neighbouring house, but nobody was hurt.
Police are linking this shooting to the petrol-bomb attack 20 minutes afterwards.
Det Insp Stewart Garrick said the "cowardly attacks" had "needlessly threatened the lives of the occupants of two addresses".
"It is essential that anyone with information does make it known, as this could so easily have resulted in a murder inquiry," he said.