We give the Yeti an oxygen machine. So the Fourth Doctor assures the Smart Daughter that he will watch the Yeti; he does this by grabbing a blanket and taking an ill-advised nap.
While he neglects his Yeti monitoring duties, Yellow Jacket guy and his Sleazy Goons do an evil mischief, removing the oxygen machine, somehow altering the warehouse the phones and getting the daughter to run away calling for help, while they Brutually Murder the Fourth Doctor.