The Bletchley Circle ended altogether too soon, a frustration that has now been largely remedied by a smart and addictive spinoff, The Bletchley Circle: San Francisco.

The Bletchley Circle: San Francisco, which premieres Thursday, July 26, as the first original series on the streaming service BritBox, takes two of the four British women from the original Bletchley miniseries and pairs them with two Americans.

So we once again have four women, all with a background in World War II codebreaking and thus highly skilled in deciphering complex patterns, applying those skills to solving crimes on which the police have given up.

While the new eight-episode drama is set in 1956 San Francisco, rather than 1952 London, our crime-solvers face the same two basic obstacles. One is the criminal, and the other is a law enforcement world in which women are not only unwelcome but openly scorned.

This is man’s work, Toots.

Returning from the original Bletchley, whose seven episodes aired in 2013 and 2014, are rebel Millie (Rachael Stirling, top and right) and librarian Jean McBride (Julie Graham, top).

That means we’ve lost Susan and Lucy, which is too bad because they had interesting personal stories it would have been intriguing to follow.

But their replacements are splendid: Iris Bearden (Crystal Balint, top) and Hailey Yarner (Chanelle Peloso, top and below).

Iris turns out to be a woman with whom Millie had exchanged messages – but never names, of course – when they were breaking code on the same side of the battle and opposite sides of the ocean during the war.

Is that ingenious or what?  

Hailey, a friend and work compadre of Iris, becomes the young kid in the group – the Lucy slot, if you will.

While Hailey is impulsive and sometimes almost a little airheaded, she’s got a brilliant mind and the same dedication as the older three.

Like its predecessor, this new Bletchley Circle is powered in significant measure by frustrated early feminism – the kind not springing from angry placard-carrying marchers, but ordinary women who didn’t enjoy having men tell them all the things they couldn’t do.  

Getting “back to normal” meant going home, raising the children, having dinner on the table every night, and keeping the house tidy. Which is fine unless it’s the only option and that’s the limit of the option.

When they did remain in the workplace, women were expected to have no aspiration higher than "secretary" and to accept crude remarks and roving hands as part of the job.   

Jean, initially resistant to getting back into the crime-solving game, makes that decision after her male superior makes it clear he will never seriously consider her for a higher career position.

The Bletchley Circle: San Francisco smartly touches on other real-life 1950s issues as well, including the leveling of old neighborhoods by politicians and developers who had visions of gleaming and profitable new cities in which all the old ragged edges were bulldozed away.

And we meet a Japanese-American woman who spent the war in an internment camp and came out of it with nothing.

All this provides rich texture for the central plotline, which has Millie, Jean, Iris, and Hailey attempting to track down a serial killer who may have murdered one of Millie’s and Jean’s friends back in London in 1942 and now seems to have resurfaced in San Francisco.

Finding a psychopathic former GI isn’t easy business, but the Sherlock Holmesian skill of these four women makes the hunt as fast-paced and fascinating as it is dangerous.

The Bletchley Circle: San Francisco spins off beautifully.

[Bonus: The second season of the original Bletchley Circle began rerunning on Monday, July 23, at 10 p.m. ET on the Ovation network and will continue for the next three Mondays at the same time.]