The Islamic State (ISIS) group threatened Britain in an Internet video Sunday showing the killing of five "spies" it said worked with the international coalition fighting ISIS in Iraq and Syria. [...] "This is a message to David Cameron," says one of the gunmen. "How strange it is that we find ourselves today hearing an insignificant leader like you challenge the might of the Islamic State." [...] "Only an imbecile would dare to wage war against a land where the law of Allah reigns supreme and where the people live under the justice and security of sharia" or Islamic law,...