The townhouse belonged to James Wilkerson, a radio station owner who had left for a vacation in St. Kitts. His daughter Cathy, a member of the Weather Underground, had borrowed the key. In the subbasement where her father restored furniture, Terry Robbins and Diana Oughton were assembling what investigators later described as the largest explosive device ever found in Manhattan. The bomb was intended for a noncommissioned officers' dance at Fort Dix, New Jersey, planned for that very evening. A second device was meant for the administration building at Columbia University.

Robbins was building the bomb his own way, unwilling to listen to suggestions from others in the group. Something went wrong. The resulting blasts killed Robbins, Oughton, and Ted Gold, who had just returned from an errand and was crushed by the collapsing facade. Two other members, Kathy Boudin and Cathy Wilkerson, were on the upper floors and survived with minor injuries. Neighbors helped the dazed, dust-covered women out of the wreckage. Both vanished before anyone thought to call the police.

Firefighters initially treated the scene as an accident, but police suspicions sharpened quickly. The two survivors had disappeared. That evening, searchers found more bombs. Over nine days, investigators sifted the rubble brick by brick, uncovering 57 sticks of dynamite, four pipe bombs packed with explosives, and 30 blasting caps, many with fuses already attached. They found timing devices rigged from alarm clocks, maps of the tunnel network beneath Columbia University, and Students for a Democratic Society literature. Had the cache detonated in the initial blast, it could have destroyed every house on both sides of the block.

Oughton and Robbins were so badly dismembered that identification required dental records. Wilkerson's parents, at the suggestion of a police detective, made a televised appeal to their missing daughter, asking her to clarify how many people remained in the ruins. The plea went unanswered. Boudin and Wilkerson had already gone underground, beginning a decade as fugitives.

The explosion became a turning point for the Weather Underground. The group had split into three cells, based in San Francisco, New York, and the Midwest, competing to carry out the boldest attacks. Machtinger's San Francisco cell had already bombed the Berkeley police headquarters on February 13, injuring several officers. The Midwestern cell had planted bombs outside Detroit police headquarters that were discovered before they detonated. The New York cell's ambitions were the most lethal.

After the townhouse disaster, surviving members confronted the reality that their recklessness had killed three of their own. They resolved to improve their technical competence. Ron Fliegelman, the one member with practical mechanical experience, became essential. He later told journalist Bryan Burrough that the Weathermen were fundamentally a group of intellectuals who did not know how to do anything with their hands. Leadership figures Bill Ayers, Bernardine Dohrn, and Jeff Jones later claimed the Fort Dix and Columbia plans were a rogue operation, with Ayers singling out Robbins.

The Wilkersons had already planned to sell the property and move to England. Nothing could be salvaged from the wreckage. Architect Hugh Hardy bought the lot for eighty thousand dollars and designed a modernist replacement with an angular front facade that broke deliberately from the block's uniform brownstone line. After eight years of delays, he sold the property at cost to David and Norma Langworthy, a Philadelphia couple, on the condition they build his design. They added extra steel reinforcement, having lost their previous home to a lightning strike.

Under the Langworthys, the house became locally famous for a different reason: the seasonally themed Paddington Bear displays Norma maintained in the front window. Every March 6, flowers appear on the sidewalk in front of the building. Bill Ayers told the New York Times in 2014 that he had placed them some years. Cathy Wilkerson eventually surrendered in 1980 and served eleven months in prison. Her father, living in Stratford-upon-Avon, told a reporter in 2000 that discussing the explosion was like talking about a bad case of poison ivy from many years ago. The two never discussed her involvement.