Mixed Reality (MR) is where digital objects can be overlaid onto real world spaces made possible by wearable headset devices such as Microsoft's HoloLens, or where digital objects are overlaid onto a mobile phone's camera image. This technology has the advantage that a user can see the real place they are in at the same time as seeing 'fictional' objects within the same space which can be interacted with. These exciting developments can be mobilised within our Museums and Heritage sites to bring to life those places and their collections, helping to interpret and animate their hidden histories. This project will develop an application of MR for the use of visitors to the Telegraph Museum at Porthcurno in Cornwall, a small museum focused on the history of transatlantic telecommunications and the site of the first telecommunication cable running between Britain and the US. We will work closely with the staff at the Museum and with the Cornwall Museums Partnership to develop an application that will help the museum to attract wider interest from a younger audience who the Museum has had difficulty appealing to. Our plan is to design a multiplayer game using MR which asks the group to solve a fictional problem that has arisen in the Museum's cable tunnels and which takes place during World War II, when the location was of extreme strategic importance. Employing techniques found in role-playing games, the participant group must find and use virtual objects within the space to solve the problems they encounter. There will be various levels of difficulty in play to help include younger people as well as older, less game literate people. We will use this premise to tell some key stories about the location and bring it to life through interaction using audio, digital objects and characterisation. Central to our plan is to engage visitors with the Museum's locale and assets as performers (playing a role in a game) thereby engaging them with its rich history. We will encounter technical and design challenges because few applications of MR have yet been used in such contexts and the more superior HoloLens headset is still beyond the reach of many users. Our intention is to record and evaluate our approaches to the challenges we encounter to be shared with other researchers in this and related areas. This knowledge has high value culturally and economically and will help the country to develop the skills and content needed to be at the forefront of MR products both in the fields of games and entertainment, as well as in education and training, healthcare and business. We also hope to deploy the excitement around a MR experience, along with the Museum's place in our technological history, to encourage greater enthusiasm for STEM-based subjects. Alongside interpreting the museum's assets for new audiences, we will also develop models and approaches that can be used by other small Museums to do the same, and we will employ methods to share our research with the sector. The project is part of a larger endeavour here in Cornwall to develop and support the growth of immersive media design, expertise and infrastructure that will link our efforts to the broader games, film and TV industry. This bid will help build expertise in the technical and design aspects of developing mixed reality applications. These are needed if we are to create meaningful and vivid interpretational applications that can extend and enrich the experience of visiting a Museum and for visitors to get the most out of the assets and collections that they hold. Even for content creators with expertise in traditional media and VR, the design methodologies for meaningful and compelling MR experiences are lacking and untested at larger scales. Technical and design challenges at the heart of this project require urgent attention if museums are to unlock the considerable power of MR to enthuse and enthral their visitors of all ages.