The husband and wife have been living under assumed names, on the run from the CIAfia and in possession of a briefcase containing documents of earth-shattering significance. It's absolutely clear that if the CIAfia find where they're holed up, they won't engage in negotiation: they'll just kill them and make off with the documents.
The couple's problem is that they've lost contact with the agency they're supposed to hand the briefcase to. They fear their usual contact has come to harm. All they can do is wait and hope that someone else in the agency knows the procedures for making contact. Husbie nips out every morning to check for the chalk mark. He always uses the proper tradecraft, so it takes him about 3 hours. And when he gets back, he always checks on exiting the lift that his wife has put a flowerpot in the pre-arranged place. If she hasn't, that will only mean one thing: she's dead and the CIAfia have taken the briefcase. In that event, he's offski: he'll turn sharp left, pay no more attention to the front door of the flat, and walk down the stairway to floor 29.
Leaving is as tense as arriving. The guys looking for them aren't gunslinging cowboys. Nobody's chances are ever 100% in this game. If they can, they'll improve their odds by entering the flat when the wife's alone. But they won't waste time. After all, when the husband goes out, the opposition could in principle make contact with him within a minute or so and he'll lead them straight up to the flat. So if possible the CIAfia will go in and kill his wife and take the briefcase as soon as he's gone out, when he's been in the lift for only a few seconds.
So every morning, she texts him. She listens for the lift door opening and closing and then she sends a text within 15 seconds. She's a professional; she doesn't forget. If she doesn't send the text, there's only one possible meaning - she's dead.
He's a professional too, but that doesn't mean he's not scared. He was trained to control his fear. He looks calmly at his watch. Five seconds. Ten seconds. By the time the lift reaches floor 12, thirty seconds have elapsed. They've killed her. Cry a tear. The CIAfia have got the documents. On to the next stage.
(He didn't receive the communication. That's the point. Let's say the man's not in danger, because the only reason the CIAfia would kill whoever's looking after the briefcase at the moment of collection is to prevent harm coming to the documents.)