Emergency services were called around 9:30pm on Tuesday 26 April following a single-vehicle collision on Ridgeway in Plympton.
The collision involved a black Harley-Davidson motorcycle and the rider, a local man in his 30s, was seriously injured.
He remains in Derriford Hospital for treatment and his injures are believed to be potentially life changing.
Police attended the scene, and the road was closed for around three-and-a-half hours while investigation work took place.
Officers are appealing for witnesses and would also like to hear from anyone who has dash cam footage which could assist with the investigation.
Anyone with any information is asked to telephone 101 or email [email protected], quoting log 887 of 26 April.
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