The White-caps--Motor Matt's Foes--Suspicious Doings--A Villainous Plot--Matt Goes Trouble-hunting--Higgins Tells What He Knows--Brisk Work at Dodge City--Matt Interviews Trueman--No. 13--Where Is Motor Matt?--Running Down a Clue--Forty-eight Hours of Darkness--At the Last Minute--The First Half of the Race--Well Won, King!--Conclusion.