The gist of this one is implied pretty well by the title - Zarkon and Co. send an invisible Robeast to Arus to take care of the Voltron Force. Coming back in a carriage after a day of picking fruit, Allura, Nanny, Lance and Pidge and some space mice are caught offguard when the invisible Robeast attacks. It overturns their carriage into a nearby lake - luckily, all are able to escape a watery fate. But before Allura can climb out of the lake, the Robeast picks her up and carries her away. After a few well placed laser blasts from Pidge's pistol, the Robeast drops Allura. However, it's not done with them. Hiding near a bluff, they're shocked to find a bolder the Robeast threw barreling toward them. Fortunately, the others at the Castle caught an inkling of what was going on and so the boulder harmlessly ends its journey on the back of Black Lion.