2x19 - Poltergeist: The Legacy

An old friend of Derek and Sloan's dies in Canada. After the funeral they think that more is involved than the authorities think. A fellow professor is snooping around, they find notes written in a language the three of them created many years ago, Derek keeps getting weird flashes and Serena, the friends wife, keeps seeing a strange creature in the triangular pond in the garden. All these things lead to Derek and Sloan staying in Canada longer than they had intended so they can investigate.