It has been nearly four years since the Somali militant group al-Shabab was forced out of the capital Mogadishu. Since then, parts of the city have started to come back to life but the security situation remains dangerous. Africa correspondent Andrew Harding returns to Mogadishu to talk to security officials charged with keeping the country safe, and to speak to al-Shabab defectors who are part of the government’s new amnesty scheme. Is Somalia turning the tide against the extremists of al-Shabab?