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: After the war he returned to Charterhouse , resigning in 1921 to take part in the first Everest expedition .