During the second season of "The Bletchley Circle," the Bletchley Park colleagues attempt to exonerate a woman accused of murder and break up an underground ring of smugglers. The second season contained two episodes, each with two installments. The show's second season aired on PBS from April to May 2014.
The first episode of the second season, "Blood on Their Hands," includes the entire original cast, including Anna Maxwell Martin as Susan. A former Bletchley Circle member, Alice, ends up in jail while awaiting trial on murder charges. Another Bletchley Circle member, Jean, suspects that Alice is covering for someone. Jean assembles the Bletchley crew, and they discover a military coverup of a chemical spill that wounded several British soldiers.
In the second episode, "Uncustomed Goods," Bletchley Circle member Millie and her business associate, Jasper, dabble in selling contraband to make extra money. When Jasper reneges on payments to the smugglers, they kidnap Millie in hopes of drawing Jasper and his money out into the open. Millie's Bletchley colleagues begin investigating after Millie vanishes and subsequently discover a sexual slavery plot, in which smugglers bring foreign girls into the country to sell them as prostitutes. Millie, Jean, Lucy and Alice alert Customs and Excise, who then intercept a contraband shipment of goods and kidnapped girls.