The Haunted Bedchamber by Gillian St. Kevern

Wiremu’s not come halfway across the world to be stopped by a ghost.
Summoned from New Zealand by his tyrannical grandfather, Wiremu arrives at isolated Scarhill House to discover scheming relatives, hostile servants, and a secretary on the verge of a nervous collapse. Little wonder: the house is inhabited by a poltergeist with an apparent grudge against Wiremu’s family.
The poltergeist isn’t the only ghost in Scarhill House. Wiremu shares his bedroom with an invisible presence. As the ghost grows increasingly familiar, Wiremu enlists the reluctant secretary Patrick’s help to uncover the secrets of Scarhill House. Can Wiremu and Patrick lay these ghosts to rest? Or will they be haunted for the rest of their lives by Scarhill’s ghosts?