He was captured soon after. At his court martial the trooper said: "While in the trenches at Armentieres I was blown up by a Minenwerfer [mortar] and was in hospital for about a month, suffering from shellshock. Up to this time I had no crimes against me. Since then my health has not been good and my nerve has been completely destroyed. I attribute my present position to this fact and to drink."
But under British military law, the 23-year-old was a coward, a disgrace, and sentenced to death.
On February 24, 1918, he was executed by firing squad.
Spencer was one of 28 New Zealand servicemen who were court-martialled and sentenced to death during World War I.
In 2000, his family's name was cleared after he was pardoned by Parliament, along with four other soldiers executed for mutiny and desertion during the war.
Now his name is etched on the Bluff War Memorial.
His war medals - the 1914-1915 Star; British War Medal (1914-1920); Victory Medal; New Zealand Certificate of Honour and Anzac Commemorative Medallion - were released to the family in 2005 and donated to the local museum.
"We are very fortunate, and very proud, to have these medals. It's a tragic local story," said Bluff Maritime Museum curator Trish Birch.
One of his descendants, former soldier Spencer Morrison, 82, said it was never talked about in his family.
"There was a level of shame surrounding it," he said.
Mr Morrison travelled to Spencer's gravesite in Belgium in 2007 to present his pardon.
"We were honoured to do that. What happened to him was simply shocking," Mr Morrison said.
"After all he went through, including we believe being buried in a trench for four days, there was no wonder he lost his marbles. It was disgusting what they did. Today, they would send them home."
100 Kiwi Stories runs every Monday and Thursday
To read the first 59 stories in this series click here.
