At the end of this month (28 March) Carcanet Press will be publishing The Golden Fleece: Essays by Muriel Spark, edited by Penelope Jardine. Please use the above web link to take you to the page which has all the details.
And at the end of April , the University of Notre Dame Press are publishing Hidden Possibilities: Essays in Honor of Muriel Spark by Robert Ellis Hosmer. The contributors include Regina Barreca, Gerard Carruthers, Barbara Epler, John Glavin, Dan Gunn,
Robert E. Hosmer Jr., Joseph Hynes, Gabriel Josipovici, Frank Kermode,
John Lanchester, David Malcolm, John Mortimer, Alan
Taylor, and John Updike and Muriel Spark's friend Doris Lessing.
Doris Lessing's obituary in The Guardian published in November last year is here and there will be a memorial service for her on 7 April at St-Martin-in-the-Fields in London.