* Series
Tudor
Murder Most Royal (1949)
The Sixth Wife (1953)
Saint Thomas' Eve (1954)
Spanish Bridegroom (1954)
Gay Lord Robert (1955)
Katharine, the Virgin Widow (1961)
The King's Secret Matter (1962)
Shadow of the Pomegranate (1962)
The Thistle and the Rose (1963)
Mary, Queen of France (1964)
Uneasy Lies the Head (1982)
Medici
Madame Serpent (1951)
The Italian Woman (1952)
Queen Jezebel (1953)
Stuart
A Health Unto His Majesty (1956)
The Wandering Prince (1956)
Here Lies Our Sovereign Lord (1957)
Murder in the Tower (1964)
The Three Crowns (1965)
Haunted Sisters (1966)
Queen's Favourites (1966)
French Revolution
Flaunting, Extravagant Queen (1957)
Louis the Well Beloved (1959)
The Road to Compiegne (1959)
Lucrezia Borgia
1. Madonna of the Seven Hills (1958)
2. Light on Lucrezia (1958)
Famous childhoods
The Young Elizabeth (1961)
The Young Mary Queen of Scots (1962)
Georgian Saga
1. The Princess of Celle (1967)
2. Queen in Waiting (1967)
3. Caroline, the Queen (1968)
4. The Prince and the Quakeress (1975)
5. The Third George (1969)
6. Perdita's Prince (1969)
7. Sweet Lass of Richmond Hill (1970)
8. Indiscretions of the Queen (1970)
9. Regent's Daughter (1971)
10. Goddess of the Green Room (1971)
11. Victoria in the Wings (1972)
Norman trilogy
1. The Bastard King (1974)
2. The Lion of Justice (1975)
3. The Passionate Enemies (1976)
Plantagenet Saga
1. The Plantagenet Prelude (1976)
2. The Revolt of the Eaglets (1977)
3. The Heart of the Lion (1977)
4. The Prince of Darkness (1978)
5. The Battle of the Queens (1978)
6. The Queen from Provence (1979)
7. Hammer of the Scots (1979)
8. The Follies of the King (1980)
9. The Vow on the Heron (1980)
10. Passage to Pontefract (1981)
11. The Star of Lancaster (1981)
12. Epitaph for Three Women (1981)
13. Red Rose of Anjou (1982)
14. Sun in Splendour (1982)
Queens of England
1. Myself My Enemy (1983)
2. Queen of This Realm: The Story of Elizabeth I (1984)
3. Victoria Victorious (1985)
4. The Lady in the Tower (1986)
5. The Courts of Love: The Story of Eleanor of Aquitaine (1987)
6. In the Shadow of the Crown (1988)
7. The Queen's Secret: The Story of Queen Katherine (1989)
8. The Reluctant Queen: The Story of Anne of York (1990)
9. The Pleasures of Love: The Story of Catherine of Braganza (1991)
10. William's Wife (1992)
11. The Rose Without a Thorn (1993)
* Novels
Beyond the Blue Mountains (1948)
The Goldsmith's Wife (1950)
Daughter of Satan (1952)
Lilith (1954)
The Unholy Woman (1954)
It Began in Vauxhall Gardens (1955)
The Scarlet Cloak (1957)
Milady Charlotte (1959) (writing as Kathleen Kellow)
Spain for the Sovereigns (1960)
Castile for Isabella (1960)
Daughters of Spain (1961)
Meg Roper, daughter of Sir Thomas More (1961)
The Captive Queen of Scots (1963)
Evergreen Gallant (1965)
The Royal Road to Fortheringay (1966)
Katharine of Aragon (1968)
Catherine De Medici (1969)
Isabella and Ferdinand (1970)
Defenders of the Faith (1971)
Captive of Kensington Palace (1972)
Queen and Lord M (1973)
The Queen's Husband (1973)
The Widow of Windsor (1974)
Mary, Queen of Scotland: The Triumphant Year (1974)
The Spanish Inquisition (1978)
Edward Longshanks (1979)
Knave of Hearts (1983)
The Judas Kiss (1983)
The Adulteress (1983)
Story of Elizabeth I (1984)
Landower Legacy (1986)
The India Fan (1988)
Melisande (1993)
Madame Du Barry (1994)
The Queen of Diamonds (1995)
The King's Adventurer: Captain John Smith And Pocahontas (1996)
* Omnibus
Charles II: Trilogy (1972)
Lucrezia Borgia: Madonna of the Seven Hills and Light on Lucrezia (1976)
Last of the Stuarts (1977)
Selected Works (1979)
* Non fiction
Growth of the Spanish Inquisition (1960)
End of the Spanish Inquisition (1961)
Triptych of Poisoners (1970)
Rise of the Spanish Inquisition (1975)
Mary, Queen of Scots: Fair Devil of Scotland (1975)