(defun pop-nth (place n)
  ""
  (let ((nth-place (nthcdr n place)))
    (prog1
        (car nth-place)
      (setcar nth-place (cadr nth-place))
      (setcdr nth-place (cddr nth-place)))))

(let ((x '(1 2 3 4 5)))
  (list (pop-nth x 3)
        x))
;; => '(4 (1 2 3 5))