The?British?Secret?Service?enlists?Tommy?and?Tuppence's?help?again?to?find?a?Soviet?agent?and?a?kidnapped?scientist.

Tommy?and?Tuppence?turn?their?attention?to?their?fellow?occupants?of?Sans?Souci?to?find?N,?the?probable?nuclear?bomb?thief.

Still?none?the?wiser?as?to?the?identity?of?Soviet?agent?'N',?Tommy?and??Tuppence?must?come?up?with?their?most?ambitious?and?risky?plan?yet?in??order?to?protect?the?lives?of?British?citizens.