Honestly, what toppled Lucius Malfoy wasn’t a single dramatic moment so much as the slow erosion of everything he’d built his identity around: influence, wealth, and being on the ‘winning’ side. Back when Voldemort first fell, Lucius slid into a comfortable role among Ministry sympathizers and old-blood cliques; that cushion let him keep snide looks and privileged protection even after the events in 'Chamber of Secrets' when he slipped Tom Riddle’s diary into Ginny Weasley’s possession. He gambled with Dumbledore’s reputation and the purity narrative, thinking power would cover any scandal.
By the time Voldemort returned and things got ugly again, Lucius’s arrogance collided with real, bloody consequences. The Department of Mysteries fiasco in 'Order of the Phoenix' was a key turning point—he failed to secure or control the prophecy, got captured, and ended up paying for that failure in Azkaban. Voldemort didn’t tolerate slip-ups from his inner circle, and old privilege suddenly meant nothing when you’d disappointed a dark lord.
After that, you can see him scramble: trying to please, trying to hide his fear, sending Draco into danger to reclaim honor. But success under Voldemort demanded ruthless effectiveness and genuine devotion; Lucius had been more about posture than conviction. In the end his fall was pride meeting consequence, with a family torn between survival and the last shreds of status. It’s tragic in a petty, very human way — like watching someone’s social currency crash and realizing reputation was all they ever had.