Crossing Europe, he battles with broken spokes, faces soaring temperatures and tackles the terrifying traffic of rush-hour Istanbul.
Having crossed Europe in just 22 days, Mark now faces the most dangerous part of his journey - one that will take him through Iran, skirting Afghanistan and across the mountains and deserts of west Pakistan. To cap it all, it's Ramadan and so food is hard to find in daylight hours.
In this leg, Mark does battle with the elements - the monsoon rains of Thailand and the scorching heat of Australia - while coping with the physical and mental effects of his epic journey.
Arriving in the USA, Mark celebrates his 25th birthday in LA but has to endure sub-zero temperatures instead of basking in the sunshine.