“We do have to be so very careful!”

“We do have to be so very careful!” is a recurring expression that connects the Beresfords’ playful performance of detective fiction with the practical caution required in their investigations. Its force shifts with context: first it marks a game between Tommy and Tuppence, then it becomes Tommy’s explanation of how he recognized a smuggling scheme concealed by a staged detective case.

A phrase between play and procedure

During breakfast, Tommy studies Tuppence as she waves a heavily buttered muffin. His grin signals that he has recognized the role-play: she is the celebrated Dr. Fortune, while he is Superintendent Bell. Tuppence explains that she has adopted the character because she feels like “a lot of hot butter.” The phrase about being careful belongs to this exchange as part of their shared theatrical code, where ordinary gestures and detective-story identities are playfully recast.

The joke depends on familiarity rather than a genuine disguise. Tommy recognizes Tuppence’s performance, and she confirms the roles instead of sustaining a deception. The same language of caution can therefore carry warmth and complicity: the partners enjoy detective conventions even when no criminal mystery is being solved.

Reading the staged scene

In the later case, Tommy repeats the phrase while explaining why he distrusted the apparent story surrounding an ambassador’s bag. He had reversed the initial question. Rather than asking why someone wanted the ambassador’s bag for an hour, he asked why someone needed another bag to be in the ambassador’s possession for that period. Diplomatic luggage would not undergo a Customs examination, making the exchange a means of smuggling something small enough to conceal in a bag; Tommy suspected drugs.

The performance in the office was part of that cover. The conspirators had responded to Tommy’s advertisement, apparently hoping to distract him or remove him from the investigation. During the staged episode, Albert performed a lasso act. Tommy noticed that the supposedly charming woman showed blank dismay at it, an expression that did not fit the role she appeared to be playing. He inferred that the stranger’s attack was designed to win his confidence in her.

Caution as a method of reversal

Tommy says that he played the credulous detective, accepted the woman’s improbable story, and let himself be lured to the beauty shop. His apparent gullibility was deliberate: he left full instructions for handling the situation, then delayed his arrival to give the others time to act. Inspector Grace and another officer met Tuppence outside; the shop had seemed genuine, and the police had not previously had cause to suspect it.

The repeated phrase thus names more than general wariness. Tommy’s method is to turn an explanation around and ask what purpose the supposedly secondary object or action serves. In the ambassador’s-bag case, the apparent target may be a decoy, while the other bag is the real instrument of the scheme. The comic breakfast exchange and the serious explanation share a principle: a detective must distinguish the role someone seems to occupy from the work that role is actually doing.

Performance and recognition

Across the book’s cases, outward identity can be manufactured through costume, behavior, and expectation. A false Inspector Dymchurch is exposed when the man’s appearance changes from that of a typical Englishman to that of a well-educated foreigner speaking English without an accent. Elsewhere, Tuppence explains how a person could pass at a distance as a woman in a long brown skirt, sweater, and hat with side curls, then change back into a man by removing those items and putting on a cap. These episodes give the expression’s warning a broader context: appearances are evidence, but they are not proof.

The phrase’s recurrence also resonates with Tommy’s insight that a sound thought to indicate someone entering a house may just as easily mean that someone has gone out. His attention to the reverse direction of ordinary assumptions helps him identify the murderer’s departure in the Gilda Glen case. Whether the clue is a door, a disguise, a bag, or a suspiciously convenient story, care means asking what else the observed fact could signify. The expression binds the partners’ comic role-playing to a recurring investigative discipline: keep the performance in view, and do not mistake it for the truth.