Image: UbisoftOfficial screenshot from Ubisoft.
A Spanner in the Works is the story achievement for completing Memory Sequence 1 of Assassin's Creed Syndicate. You earn it by finishing the opening sequence, which introduces both twins in separate memories: Jacob at an ironworks in Croydon and Evie in her own infiltration.
Play the main memories of Sequence 1 through to the end. Optional objectives do not matter for this one; only the 100% sync achievement, Mentor, asks for those.