Odd Apocalypse by Dean Koontz

Odd Apocalypse: An Odd Thomas Novel - Odd Thomas and Annamaria, who he met in Magic Beach, have been invited to stay at Roseland. Although they are invited guests, no one at the estate really knows why they are there and resent their presence.  At night they are told to stay inside and lock the doors because of the mountain lions.  But the sounds that Odd hears at night are not those of mountain lions.  As he is walking the estate he meets a lady on a horse who indicates to him that he needs to help someone on the estate who is in danger.  He also experiences odd events such as seeing two opposing shadows of the stable and being chased by weird creatures in the middle of the day.