They were to be dropped off in London, with a map and very few clues. The person they were to make contact with was given the name of Ted Brown; other than that, they had his last-known address and his line of work – a butcher. His story was that he was running a branch of the underground and would be valuable to them.

‘Let’s treat it like a game, Sibbie. See who can unearth the most clues about our Mr Brown.’

When they tracked him down, they found that Mr Brown was being kept prisoner. The last time he’d been seen he was being taken into a flat above a shop. They decided they would wait until nightfall and then break into the shop and rescue him. They only had hours left to report that they had made contact.

All was going well. Sibbie had managed to ‘pick the lock’ and they were inside the shop. Using torches, they found their way to a door that looked likely to lead upstairs, when suddenly the ringing of bells, indicating that a police car was approaching, had them standing like statues, unsure whether to run or to continue their mission.

‘What if these were Germans coming after us – what would we do?’ Marjie’s voice shook as she asked Sibbie.

‘Run. Run as fast as we can and try to outwit them, and of course fire our guns at them, but we can hardly do that here.’

‘Not unless we do it as we did when practising . . . Bang, bang!’

Sibbie muffled the laugh that wanted to burst out of her. That Marjie could make her laugh at such a time boded well. For at this moment they were in a sticky situation.

‘We could call in. We have an emergency number, and HQ will explain to the police.’

‘No, Marjie. I think this is part of the test. Come on, they’re getting nearer.’

Both girls shot out of the door, almost tripping each other over. Running like the wind, they made it to the end of the street before the police pulled up outside the shop.

‘The Germans won’t warn us by ringing a bell, you know.’

‘Yes, I heard they were mean like that.’

‘Oh, Marjie, stop it. This is serious!’ Despite Sibbie’s mock reprimand, they giggled, as much from relief at not being caught as anything else.

‘We still haven’t made contact. Shall we hang around and see if the police leave, when they see they haven’t caught anyone red-handed?’

Before she had time to say yes or no, Marjie came up with a good plan. ‘I know, let’s walk along the street as if we are going about our normal business. We can say we know the man who lives there, and would the police see if he is all right?’

‘Brilliant. Right, best foot forward, and charm to the ready.’