A leash and collar system for a pet, having a unique coupling that can be quickly attached and detached with one hand, even while the coupling is pulled in tension. The coupling has a female section and a male section that selectively interconnect. The female section defines a receptacle for receiving the male section. A magnet is disposed within the receptacle at its base. The male section has an internal plunger element that selectively moves between a forward position and a rearward piston. When the male section is inserted into the female section, the plunger element is magnetically attracted to the magnet in the receptacle. The magnet pulls the plunger element into its forward position. Locking elements protrude from the male section when the internal plunger element is in its forward position. The locking elements prevent the male section from being retracted out of the receptacle.