Witnesses say the party was under way when someone drove by and opened fire.
The shooting happened about 5 p.m. in the 5100-block of S. May in the Back of the Yards neighborhood.
A warm late spring night, a party for a prom, and a celebration to mark a young rapper's ascent lending an air of hope to a tough part of the city and then suddenly there were gunshots, and two young men had their futures ended.
Q is the 17th letter in the alphabet, marking the last bullet shell Chicago police found when they responded to a call of shots fired in Englewood Friday night.
The balloons were arranged for Sonya Stephanie, heading off for prom, but instead witnessing the death of her big brother, 22-year-old Marshawn Stephanie, and a 26-year-old man, struck down by unknown assailants.
"We live right here," said Sonya Stephanie. "They came shooting in front of our house. My brother wasn't going to be in no mad gang."
Friends and family said Marshawn was as much a part of the festivities for publishing on YouRube a video under his stage name, Kamakazi-Mazi. Many who saw him die were in the video, filmed last week in Englewood.
"He was a good person never like get in trouble, he had no fights, none of that," said Shaquita Triplett. "He just always had his little sister.He was the oldest."
Several onlookers who declined to be interviewed on camera said they suspected the shooters were from a few blocks away, locked in a retaliatory battle with May Street area residents over previous killings.
Stopping Englewood's epidemic of such violence was the focus of a CeaseFire meeting 1.5 miles from the incident.
"Our target population is the ones who are most likely to shoot or be shot, but more so, what we are trying to bring in is more people to be involved because everybody is likely to be shot," said CeaseFire program director James Highsmith.
"He was trying to be a rapper, he don't gang-bang," Sonya Stephanie said. "He's my big brother, I don't got no one else. Got nobody but my brother."
Chicago police confirm three other young men were shot. Two were treated at Stroger Hospital. One is in serious to critical condition. The other had a hand injury and was taken to provident hospital.
Police have made no arrests.