'Missing Train' is the short form often colloquially used when referring to the Andrew Greeley novel 'The Bishop and The Missing L Train.' With short assignments such as the one in your heading, it is usually a succinct precis that is required so do not try to retell the whole story. Just try to encapsualte the bare bones of the plot - a short summary if you like. For example you could say how the story concernsThe Vatican and it's decision to assign an auxiliary Bishop to the Archdiocese of Chicago against the aggressively stated wishes of Archbishop Cronin, and also ignoring protests from Bishop Blackie. Bishop Quill merrily thinks he has been specially sent by Rome as a perfect and hand-picked choice to replace the Cardinal when actually the Vatican couldn't wait to see the back of him because of his complete 'idiocy.' The minute he gets to Chicago, he disappears while travelling aboard the L Train and Bishop Blackie is charged with  finding him. You could maybe add one quote, for example  "The Vatican does not like to lose bishops, even auxiliaries" as that one shows the lighthearted humour and a suggestion of what the rising action will be like - perhaps a recipe for a little suspense and some hilarity.