diff --git a/advent-of-code-2018.asd b/advent-of-code-2018.asd
index c2c9fc2..d99de5f 100644
--- a/advent-of-code-2018.asd
+++ b/advent-of-code-2018.asd
@@ -27,4 +27,5 @@
                (:file "day17")
                (:file "day18")
                (:file "day19")
-               (:file "day23")))
+               (:file "day23")
+               (:file "day25")))
diff --git a/day25.lisp b/day25.lisp
new file mode 100644
index 0000000..62e1800
--- /dev/null
+++ b/day25.lisp
@@ -0,0 +1,17 @@
+;;;; day25.lisp
+
+(in-package :advent-of-code-2018)
+
+(defun day25-make-in-range-p (p1)
+  (lambda (p2) (<= (manhattan p1 p2) 3)))
+
+(defun day25 ()
+  (loop
+    :for p :in (mapcar #'extract-integers (read-puzzlefile "input25.txt"))
+    :for sets := (list (list p)) :then (loop :for set :in sets
+                                             :if (some (lambda (p2) (in-range-p p p2)) set)
+                                             :append set :into in-range
+                                             :else
+                                             :collect set :into other
+                                             :finally (return (cons (cons p in-range) other)))
+    :finally (return (format t "There are ~a constellations.~%" (length sets)))))