Complex sentence: Reacher's maternal grandfather Laurent Moutier was a furniture restorer in Paris, who, at hirty years of age, volunteered for the French Army in 1914 at the outbreak of World War I, fighting at Verdun and The Somme.
Split into simpler sentences: Reacher's maternal grandfather Laurent Moutier was a furniture restorer in Paris. Thirty years old in 1914, he volunteered for the French Army with the outbreak of World War I and fought at Verdun and The Somme.