Barty Crouch Jr. is secretly rescued from Azkaban

His mother uses Polyjuice Potion to take his place there, where she dies within a year (GF27). Crouch Jr. is kept a virtual prisoner in his father’s home, tended by Winky, a loyal house-elf (GF35).

Timeline Notes

We know from Sirius Black in GF27 that the escape was "about a year" after Crouch Jr. had been sent to Azkaban, so it was probably sometime around November or December of 1982 [Y2].