[4][5] Writer and producers Mark Hayhurst and Sue Horth compiled a 175-page book tracing "every conference, every telephone call, private letter and telegram swirling around Europe" before writing the script.

In a four-star review for The Times, Andrew Billen called the series "a clear and often brilliant dramatisation" and praised McDiarmid's portrayal of Grey as "surely one of the actor's greatest performances" though he found "the humour becomes slightly broader" in the scenes set in Berlin and Vienna and that the subplot of the two clerks "rather peters out".

[8] In a four of five-star review for The Telegraph, Christopher Howse found the series "enthralling" but was distracted by the use of the Belfast City Hall as a location for Whitehall.

[9] Andrew Anthony of The Guardian called the series a "meticulous rendering" and "impressively wordy and careful imagining" free of "romantic digressions or fictional appeals to sentiment", with a "strong performance" by McDiarmid; he also found the drama "rigid and simplistic" with "dubious stereotypes and an excess of rhetorical dialogue".

[10] In The Independent, Ellen Jones wrote the series' "masterstroke" was "to reframe this history textbook timeline as a subtle character study", praising its "terrifically well written" dialogue.