After a four-year hiatus, the classy code-breaking drama is back - and heading to San Francisco!

The Bletchley Circle spin-off, The Bletchley Circle: San Francisco, will start on Wednesday 25th July at 9m, ITV has revealed.

The original series, which ran from 2012 to 2014, saw Anna Maxwell Martin, Julie Graham, Sophie Rundle and Rachael Stirling play four former code-breakers at the famous World War II code-breaking centre Bletchley Park, who joined forces to solve complex crimes.

Now, Rachael and Julie reprise their roles as Millie and Jean in The Bletchley Circle: San Francisco.

The action moves to 1956 and ballsy map-reader Millie and no-nonsense Jean will head across the pond to join forces with two American codebreakers, Iris (played by Crystal Balint) and Hailey (Chanelle Peloso), to investigate a string of murders.

The trailer shows the pair teaming up and using their codebreaking skills once more. Explaining what they’ll be up to, Julie Graham’s character says: “The same thing we did in the war. Crack codes. Tease out information. Recognise patterns.”

Talking to us about the series, Julie told us: “Essentially Millie and Jean go to San Francisco to help out an old Bletchley colleague. There was actually a code breaking station in San Francisco, which eventually expanded into the Cold War.”

Another chance to catch the first series of this cracking crime drama.

The original Bletchley Circle series proved popular with viewers, who’ll no doubt want to catch the new series

The Bletchley Circle: San Francisco is four parts.