"Then when shall we start?" asked the pilot. "Now," decided the Sub promptly. Both men were warming to their work. Even if the desired result were not forthcoming, it was something to occupy their minds, and to ward off the deadly monotony. "We'll have to go slow," cautioned Seton. "The floor looks pretty solid, and we've no tools." "Haven't we, by Jove!" exclaimed Smith, producing a steel marline-spike of about nine inches in length. "I saw this beauty in the boat that brought me across the harbour, and, thinking it might come in useful, I annexed it. We'll start with this stone; it looks slightly wonky." While one listened at the door for the sentry, the other tackled the cement. Working in turns, they succeeded at the end of three hours' work in prising the slab from its bed. Underneath was a quantity of rubble, bordered on one side by a stone slab. "We're breaking into the old trap-hatch," declared the pilot. "We must clear this rubble and get rid of it. I vote we carry on till supper-time, and then stand by till midnight. It will be a slow business at first." Handful by handful the rubble was removed, and thrown cautiously through the window on the seaward-side of the Mole. Before supper was brought in, the stone slab that formed the only barrier between the cell and the arch of the communication gallery was exposed. In good time the upper slab was replaced and dust rubbed into the exposed joints, so that the gaoler would not notice anything was amiss. "To-night's the night," remarked Smith, as the two prisoners partook of their frugal, unappetizing meal. "We'll have a jaunt ashore, if nothing else." "What day is it?" asked Alec. "I've lost all count of time." "Twenty-second of April," replied the pilot. "Good enough!" exclaimed Seton joyfully. "St. George's Eve--a good omen." As night fell the two officers prepared to renew their task. If Smith's surmise were correct, the actual business of breaking out of their cell seemed a fairly simple matter. Seton wondered why he had not thought of a similar plan before. Then he reflected that, had he done so, and had the work of getting clear of the Mole been successful, he would most certainly have attempted to make for the open sea. The idea of bluffing the Hun by going inland and thence across the Dutch frontier had never occurred to him. Nevertheless the whole business was fraught with peril. The men were liable to be shot at sight by the sentries; if recaptured they might also be executed as spies, since they were not in uniform. Without doubt Count Otto von Brockdorff-Giespert would not be backward in taking any steps to make it decidedly unpleasant for them should they have the ill-luck to be recaptured.