[Footnote 10: Tri-chess: a highly involved game of tri-dimensional chess played on a series of eight superimposed glassine boards. Pieces move not only horizontally, as in the ancient Persian game, but vertically as well. Two additional types of pieces are used in conjunction with the traditional "pawn, knight, bishop," et al. ... the "pilot," which may move in any direction horizontally or vertically until opposed by another piece, and the "ranger," which may move five vertical spaces and three horizontal, or vice versa, disregarding occupants of those squares.--_Ed._] "I think--" Hugh Warren had risen abruptly to his feet as a light flashed on the signal panel before them--"I think we won't have to worry about that problem. The Magogeans seem to have already contacted _us_! See that warning? It means there is someone at the airlocks." "Then quickly," snapped Gary, "turn on the force-shield, Hugh!" Dr. Kang shook his head. "It is too late, now. If invaders have lighted the warning signal they are already inside the protective envelope." He turned worried eyes to the space patrolman. "What shall we do, Captain?" "There's only one thing _to_ do," grunted Warren. "Find out who it is, then blast them to hell-and-gone out. Hawkins!" He bawled the name out over the audio. A moment later the little cockney steward bustled into the turret. "Comin' hup, Captain. You called me?" "Yes. Break open the ordnance lockers. Supply every man aboard with arms. I'm afraid we have visitors." Hawkins grinned impishly. He didn't scare easily. "Right, Cap'n. Side arms all around it is, sir." And he scampered away as Warren turned to his companions. "All right. Let's go have a little look-see at our unexpected guests." Moments later they were standing in the companionway beside the fore sta'b'rd lock. As the turret's warning system had advised, someone was outside the ship. A duplicate signal, activated by electric eye, was flashing on the airlock's inner port. Not only that, but through the aerated protection chamber could be heard faint noises of someone rapping or fumbling with the exterior controls. O'Day nodded at Lane significantly. "Magogeans, all right. But our pal Borisu's not with them. He'd know how to operate the lock from outside. They don't." Gary said tightly, "Well, since the mountain can't come to Mohammed--" and drew down the lever which opened the inner port. The noises were clearer now. In addition to the scrabbling sound there were faint murmurs, a low babble of indistinguishable voices. Warren glanced swiftly at instruments on the airlock wall, nodded to his companions. "Gravity and atmosphere O.Q. We're adjusted to the first by our changed size, I guess, and the second approaches Earth's normal. Everybody set? I'll throw open the outer door. The minute you see them, let 'em have it."