The Road to Hell is Paved with Parsnips - Housetrap, #10

Randy's old, sometimes good buddy, Charlie is accused of murder most foul and Randy and Bertha must stash him away from the fingers of the law and discover the truth. What they uncover are parsnip hijackings and strange goings-on, vegetable cartels, and demons. While north to the parsnip fields Randy falls into the clutches of Freydis, the queen of the Huldufolk, who don't usually take kindly to strangers.
She's willing to make an exception for Randy if he signs their agreement in blood. All he has to do is rescue several loads of parsnips from an army of villains, get the vegetables back to the city in time for the Annual Parsnip Festival, discover who the mastermind behind the hijackings is, and clear Charlie's occasionally good name.