midnight
They were too intent on their mission , however , to realize that anything out of the ordinary was going on aboard the houseboat . A whispered conversation ensued in the rowboat , then two boys got cautiously to the deck of the cockpit . There followed a period of silence and a low-spoken command from below . A mighty yell suddenly broke from the midnight visitors . Howls and shrieks , Indian war-whoops and beating on the cabin with sticks , accompanied the shouts . `` Pirates ! Surrender ! ''