While investigating an explosion that kills two people, Sherlock discovers a crime that’s been lying dormant for years. Meanwhile, Watson encourages Sherlock to finally pick a sponsor.

Thackery weighs performing surgery on a former flame, and orders Gallinger and Chickering to experiment on pigs. Barrow goes the extra yard to square a debt. After a bad day…

The pressure starts to affect Axe. Chuck uses the past to his advantage.

When Erin tries to take down a gang leader using his law-abiding brother as bait, the family debates her methods.