Original: During British Mount Everest Expedition 1924 , the third British attempt on the world 's highest mountain , Mallory and his climbing partner Andrew Irvine both disappeared somewhere high on the North-East ridge during their attempt to make the first ascent or descent of the world 's highest mountain .
Simplified: Mallory and his climbing partner Andrew Irvine both disappeared somewhere high on the North - East Ridge in an attempt to get to the top .