It’d be easy to glance at “Truth Seekers” and mistake it for a satirical farce. The new Amazon series comes from Nat Saunders, James Serafinowicz and the vaunted duo of Nick Frost and Simon Pegg, who have collaborated on genre comedies like “Shaun of the Dead” and “The End of the World.” Starring Frost as a wireless service repairman slash amateur paranormal investigator, “Truth Seekers” has plenty of small-town British charm to spare as he travels from one haunted house to another. But the series also quickly reveals itself to be a genuinely creepy bit of horror, with ghost stories that are tragic and poignant, startling and violent. It channels everything from “The Exorcist” to “Doctor Who” to create set-pieces that stick with you after the credits have rolled, keeping the show from getting stuck in a single comedic gear.