By the time Senior Special Agent Sam Richardson’s team rolled up to the small house on Lark Ellen Avenue in a cool twilight, it had little to show for several hours of work.

The stops in San Dimas and Covina: no luck. At the gray house on a corner in Pomona, yes, Nohemi Page was home with her infant. But the four pistols registered in her name — guns that felony convictions in California now rendered illegal for her to possess — were long gone.

When Page went to drug rehab, her aunt placed her belongings in a storage unit, then stopped paying the monthly fee. The guns, as elusive as quicksilver in a country awash in weapons, now belonged to whoever bought the contents in a blind auction.

But the “knock and talk” at the house here, with Brenda Rivera, a 56-year-old grandmother with a felony theft conviction and a registered firearm, spun out differently. After a confused but calm hour and a half, the team had its first tangible success of the day. A pistol, the magazine missing. A hard-won trophy for a unit at the sharp, streetside edge of America’s debate over who should own guns and who should not.