August Spies's last evening on earth as a free man was fraught with difficulty and confusion, even before the Haymarket bomb exploded in the middle of Desplaines Street. Thinking he would be one of the German speakers, who usually followed those who addressed such rallies in English, Spies did not leave his home near Wicker Park until a little after 7:30, the time the demonstration was scheduled to begin. He walked there with his brother Henry.

Because of its uncomfortable bulk, Spies decided to leave his revolver with a friend. At the trial, he explained why he usually carried this weapon with him: "I was out late at night, and I always considered it a very good thing to be in a position to defend myself." He entrusted the gun to Frank Stauber, the socialist alderman whose experience with election fraud in 1880 had influenced Spies's decision to embrace anarchism and cease trying to work within the system.

As an invited speaker, Spies had no idea that it would fall to him to organize the rally on the spot. When he arrived, there was no meeting, only a lot of people milling around. He made a brief and unsuccessful search for Albert Parsons, whom someone told him was spotted nearby, and then returned to call the crowd together. Before this, he had commandeered a long express wagon (there were actually two wagons) half a block up Desplaines Street from Randolph on the east side of the street, right above an alley that ran along the south side of the Crane Brothers factory, where plumbing supplies were manufactured.

When someone suggested that they pull the wagon down to Randolph and into the Haymarket area proper, Spies decided to stay put, since he was concerned that the rally might then interfere with traffic on Randolph and that the noise from the street cars would be distracting. Spies spoke to the crowd of about one thousand in English, having sent Balthasar Rau to the Arbeiter-Zeitung building to see if he could find more speakers. The American Group of Chicago anarchists was holding a special meeting that evening in the Arbeiter-Zeitung offices on the subject of organizing sewing girls.

The Arbeiter-Zeitung had received a call earlier in the evening requesting that Spies speak at an eight-hour rally at the Deering Harvester works on the North Side, where workers had walked out in a strike for the eight-hour day. Michael Schwab, who had been at the Arbeiter-Zeitung, headed for the Haymarket to look for Spies, who had not yet arrived. Schwab conversed briefly with Rudolph Schnaubelt, Schwab's brother-in-law, then traveled by streetcar back downtown and transferred to a Clybourn Avenue car that took him to the Deering rally. He spoke at the rally, had a beer in a saloon, and returned home.

Parsons and Fielden agreed to Rau's request to join Spies as speakers at the Haymarket meeting. Parsons had returned only a few hours earlier from an eight-hour movement meeting in Cincinnati. Fielden, a teamster, had begun his day hauling a load of stone the ten miles to Waldheim Cemetery in Forest Park, where all the Haymarket accused except Fielden himself would eventually be buried. Neither Parsons nor Fielden learned about the Haymarket meeting until shortly before it began.

The two men hastened to the Haymarket, followed by several others, including Lucy Parsons, Lizzie Holmes, and the Parsons' two children. When Spies saw Parsons and Fielden arrive, he finished his address. Parsons delivered a speech, and was followed by Fielden. Lucy Parsons meanwhile took a seat with some others on the second wagon, a few feet further north on Desplaines Street.

Fielden began to speak around ten o'clock. The weather had turned chilly, rain seemed likely, and only a few hundred spectators remained. Parsons, who had joined his family and other friends on the second wagon, interrupted Fielden to suggest that they move to Zepf's Hall, a half block away, on the northeast corner of Lake and Desplaines Streets. With the meeting drawing to a close, however, Fielden said that he would quickly conclude his remarks and end the meeting.

At this point, the police assembled by Inspector John Bonfield at the nearby Desplaines Street police station set out to disperse the rally. When they arrived in front of the speakers' wagon, Captain Ward ordered that the rally end "immediately and peaceably." Fielden stated that the meeting was peaceable, and Ward repeated his order. Police Lieutenant Martin Quinn, one of the officers on the scene, claimed in his official report that Fielden had previously said, "There are the bloodhounds coming, you do your duty and I will do mine." Quinn gave very similar testimony in court. Fielden and others disputed this, as they did many other details of the police testimony. Some of the officers stated, for example, that Fielden started shooting at the police, whereas Fielden maintained that he never owned or fired a gun in his life.

What was beyond dispute was that moments after Ward repeated his command order, someone threw the Haymarket bomb directly into the ranks of the police from a point on the sidewalk on the east side of Desplaines Street.